New benzimidazolylpyridazinones of the formula I ##STR1## in which R.sup.1 is a styryl or mononuclear of binuclear heteroaryl radial which contains 1-4 heteroatoms, each of which is unsubstituted or singly or multiply substituted by alkyl, alkoxy, alkylthio, halogen, OH, SH, amino, alkylamino, dialkylamino, acylamino having 1-8 C atoms, nitro, COOH, COOalkyl and/or CN, PA0 R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each H or alkyl, and PA0 R.sup.6 and R.sup.7 are each H, or together are a C--C bond, PA0 and in which the alkyl and alkoxy groups each contain 1-4 C atoms, and their salts, show positive inotropic, vasodilating and antithrombotic actions.

BACKGROUND OF THE INVENTION 
The invention relates to new benzimidazolylpyridazinones. 
Similar compounds are disclosed in German Offenlegungsschrift No. 
2,837,161. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide new compounds with valuable 
properties, in particular those which can be used for the preparation of 
medicaments. 
Upon further study of the specification and appended claims, further 
objects and advantages of this invention will become apparent to those 
skilled in the art. 
These objects have been achieved by providing new 
benzimidazolylpyridazinones of Formula I 
##STR2## 
in which R.sup.1 is a styryl or mononuclear or binuclear heteroaryl 
radical which contains 1-4 heteroatoms, each of which is unsubstituted or 
singly or multiply substituted by alkyl, alkoxy, alkylthio, halogen, OH, 
SH, amino, alkylamino, dialkylamino, acylamino having 1-8 C atoms, nitro, 
COOH, COOalkyl and/or CN, 
R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each H or alkyl, and R.sup.6 and 
R.sup.7 are each H, or together are a C--C bond, 
and in which the alkyl and alkoxy groups each contain 1-4 C atoms, 
and to their salts. 
DETAILED DISCUSSION 
It has been found that the compounds of the formula I and their salts have 
valuable pharmacological properties while being well tolerated. In 
particular, they exhibit an effect on the force of myocardial contraction 
(positive inotropic activity); furthermore, the substances have 
vasodilating action and thus promote blood flow. The vasodilating action 
and the action on the heart can be determined on, for example, 
anaesthetized or conscious dogs, cats, monkeys or mini-pigs, and the 
positive inotropic action can be determined on isolated heart preparations 
(for example the atrium, papillary muscle or perfused whole heart) of the 
rat, guinea-pig, cat or dog, for example by methods as are described in 
Arzneimittelforschung, Volume 31 (I) No. 1a (1981), pages 141 to 170, or 
by Schliep et al. in 9th International Congress of Pharmacol., London, 
Abstracts of papers 9P. 
Furthermore, they have antithrombotic properties and properties inhibiting 
platelet aggregation and affecting the shape of erythrocytes. The effect 
on platelet function in the sense of inhibition of aggregation can be 
demonstrated in the rat in the Born ex vivo test (Nature 194, 927-929, 
1962). The antithrombotic action is shown by the prolongation of the 
bleeding time by the method of Stella (Thrombos. Res. 7, 709-716, 1975), 
in the reduction in the thrombus weight on cold-induced thrombosis of the 
jugular vein in the rat by the method of Meng (Ther. Ber. 47, 69-79, 
1975), and in the increase in the laser pulses necessary for complete 
thrombosis in the mesenteric venule of the rat, corresponding to a 
modification of the method of Kovacs (Microvasc. Res. 6, 194-201, 1973). 
The favorable action on erythrocyte deformability is detectable by the 
method of Schmid-Schobein with nucleopore filters (Pfluger's Archiv 338, 
93-114, 1973). In addition, favorable effects on 
fibrinolysis/euglobulinlysis time can be detected by the method of v. 
Kaulla (Progr. Chem. Fibrinol, Thrombol. 1, 131-149, 1975; ed. J. F. 
Davidson, Raven Press, N.Y.). 
The compounds can thus be used as active compounds in medicaments in human 
and veterinary medicine. Furthermore, they can be used as intermediates 
for the preparation of other active compounds for medicaments. 
In the formulae, alkyl is preferably unbranched, preferably has 1-3 C 
atoms, and is preferably methyl, and is also preferably ethyl or propyl, 
furthermore isopropyl, butyl, isobutyl, sec.-butyl or tert.-butyl. 
Alkoxy is preferably unbranched, preferably has 1-3 C atoms and is 
preferably methoxy, and is also preferably ethoxy or propoxy, furthermore 
isopropoxy, butoxy, isobutoxy, sec.-butoxy or tert.-butoxy. Alkylthio is 
preferably unbranched, preferably has 1-3 C atoms and is preferably 
methylthio, and is also preferably ethylthio or propylthio, furthermore 
isopropylthio, butylthio, isobutylthio, sec.-butylthio or tert.-butylthio. 
Halogen is preferably F or Cl, but is also Br or I. Alkylamino is 
preferably methylamino, and is also preferably ethylamino or propylamino, 
furthermore isopropylamino, butylamino, isobutylamino, sec.-butylamino or 
tert.-butylamino. Dialkylamino is preferably dimethylamino, and is also 
preferably methylethylamino, diethylamino or dipropylamino, furthermore, 
for example, diisopropylamino, dibutylamino, diisobutylamino, 
di-sec.-butylamino or di-tert.-butylamino. Acylamino is preferably 
alkanoylamino having 1-8 C atoms, for example formamido, acetamido, 
propionamido, butyramido, isobutyramido, valeramido, hexanamido, 
heptanamido and octanamido, and is also preferably benzamido, substituted 
benzamido, for example o-, m-, or p-methylbenzamido, o-, m- or 
p-methoxybenzamido, 3,4-dimethoxybenzamido, o-, m- or 
p-methylthiobenzamido, o-, m- or p-fluorobenzamido, o-, m- or 
p-chlorobenzamido, o-, m- or p-bromobenzamido, o-,m- or p-iodobenzamido, 
o-, m- or p-aminobenzamido, o-, m- or p-methylaminobenzamido, o-, m- or 
p-dimethylaminobenz-amido, o-, m- or p-nitrobenzamido, o-, m- or 
p-carboxy-benzamido, o-, m- or p-cyanobenzamido, and is also preferably 
unsubstituted or substituted picolinamido, nicotinamido or 
isonicotinamido. COOalkyl is preferably methoxycarbonyl or ethoxycarbonyl, 
furthermore propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, 
isobutoxycarbonyl, sec.-butoxycarbonyl, or tert.-butoxycarbonyl. 
When R.sup.1 stands for a substituted styryl or heteroaryl radical, the 
total number or heteroaryl radical is 1 to 5, preferably 1 or 2. 
The possible substituents on the mentioned benzamido group include all of 
those mentioned for R.sup.1 per se except for acylamino. The total number 
of substituents on the benzamido group is typically 0 to 5, preferably 0 
to 1. 
The mononuclear or binuclear heteroaryl radicals typically are of 3 to 14, 
preferably 5 to 10 ring atoms in total, each ring containing from 3 to 8, 
preferably 5 or 6 ring atoms in total, there being from 1 to 4, preferably 
1 or 2 hetero atoms in each ring. Suitable hetero atoms include O, N and 
S. 
Specifically, R.sup.1 is preferably styryl which is unsubstituted or 
substituted as indicated, or 1-, 2- or 3- pyrryl, 2-or 3-furyl, 2- or 
3-thienyl, 2-, 3- or 4-pyridyl, 2-, 4- or 5-thiazolyl, 3-, 4- or 
5-isothiazolyl, 1-, 3-, 4- or 5- pyrazolyl, 1-, 2- or 4(5)-imidazolyl, 2- 
4- or 5-oxazolyl, 3-, 4- or 5-isoxazolyl, 1,2,4-triazol-1-, -3- or -5-yl, 
1,3,4-thiadiazol-2-yl, 1- or 5-tetrazolyl, 3- or 4-pyridazinyl, 2-, 4- or 
5-pyrimidyl, pyrazinyl, 2-, 3-, 4-, 5-, 6- or 7-indolyl, 2-, 3-, 4-, 5-, 
6- or 7-benzofuryl, 2-, 3-, 4-, 5-, 6- or 7-benzothienyl, 2-, 3-, 4-, 5-, 
6-, 7- or 8- quinolyl, 1-, 3-, 4-, 5-, 6-, 7- or 8-iso-quinolyl, 2-, 4-, 
5-, 6- or 7-benzothiazolyl, 1-, 2-, 4-, 5-, 6- or 7- benzimidazolyl or 2-, 
6- or 8-purinyl which is unsubstituted or substituted as indicated. 
Individual preferred substituted radicals R.sup.1 are o-, m- or 
p-methylstyryl, o-, m- or p-methoxystyryl, o-, m- or p-ethoxystyryl, 2,3-, 
2,4- 2,5- 2,6-3,4- or 3,5-dimethoxystyryl, 3,4,5-trimethoxystyryl, o-, m- 
or p-methylthiostyryl, o-, m- or p-ethylthiostyryl, o-, m- or 
p-fluorstyryl, o-, m- or p-chlorostyryl, o-, m- or p-bromostyryl, o-, m- 
or p-iodostyryl, o-, m- or p-hydroxystyryl, o-, m- or p-mercaptostyryl, 
o-, m- or p-aminostyryl, o-, m- or p-methylaminostyryl, o-, m- or 
p-ethylaminostyryl, o-, m-or p-dimethylaminostyryl, o-, m- or 
p-diethylaminostyryl, o-, m- or p-formamidostyryl, o-, m- or 
p-acetamidostyryl, o-, m- or p-benzamidostyryl, o-, m- or p-nitrostyryl, 
o-, m- or p-carboxystyryl, o-, m- or p-methoxycarbonylstyryl, o-, m- or 
p-ethoxycarbonylstyryl, o-, m- or p-cyanostyryl, 1-methyl-2-pyrryl, 
1-methyl-3-pyrryl, 3-, 4- or 5-methyl-2-furyl, 3-, 4- or 5-fluoro-2-furyl, 
3-, 4- or 5-chloro-2-furyl, 5-bromo-2-furyl, 5-nitro-2-furyl, 3-, 4- or 
5-methyl-2-thienyl, 3-, 4- or 5-fluoro-2-thienyl, 3-, 4- or 5- 
nitro-2-thienyl, 3-, 4- or 5-dimethylamino-2-thienyl, 3-, 4- or 
5-formamido-2-thienyl, 2-, 4- or 5-methyl-3-thienyl, 3-, 4-, 5- or 
6-methyl-2-pyridyl, 3-, 4-, 5- or 6-fluoro-2-pyridyl, 3-, 4-, 5- or 
6-chloro-2-pyridyl, 2-, 4-, 5- or 6-methyl-3-pyridyl, 2-, 4-, 5- or 
6-fluoro-3-pyridyl, pyridyl, 2-, 4-, 5- or 6-chloro-3-pyridyl, 2-, 4-, 5- 
or 6-hydroxy-3-pyridyl, 2-, 4-, 5- or 6-dimethylamino-3-pyridyl, 2-, 4-, 
5- or 6-formamido-3-pyridyl, 2-, 4-, 5- or 6-acetamido-3-pyridyl, 2- or 
3-methyl-4-pyridyl, 2- or 3-fluoro-4-pyridyl, 2- or 3-chloro-4-pyridyl, 
2,6-dichloro-4-pyridyl, 4- or 5-methyl-2-thiazolyl, 5-nitro-2-thiazolyl, 
2- or 5-methyl-4-thiazolyl, 2,4-dimethyl-5-thiazolyl, 4- or 
5-methyl-3-isothiazolyl, 3- or 5-methyl-4-isothiazolyl, 4- or 
5-methyl-3-pyrazolyl, 4- or 5-methyl-2-imidazolyl, 2- or 
5-methyl-4-imidazolyl, 4- or 5-methyl-2-oxazolyl, 2- or 
5-methyl-4-oxazolyl, 2- or 4-methyl-5-oxazolyl, 4- or 
5-methyl-3-isoxazolyl, 3- or 5-methyl-4 -isoxazolyl, 3- or 
4-methyl-5-isoxazolyl and 5-methyl-1,3,4-thiadiazol-2-yl. 
Particularly preferred radicals R.sup.1 are 2-, 3- or 4-pyridyl, also 2- or 
3-thienyl, 2- or 3-furyl, 1-methyl-2-pyrryl, styryl, p-dimethylaminostyryl 
or 3,4-dimethoxystyryl. 
R.sup.2, R.sup.4 and R.sup.5 are each preferably H or CH.sub.3 ; in 
particular R.sup.2, R.sup.4 and R.sup.5 are preferably H. R.sup.3 is 
preferably H, CH.sub.3 or C.sub.2 H.sub.5, in particular CH.sub.3. 
R.sup.6 and R.sup.7 are each preferably H. 
The invention particularly relates to those compounds of the formula I in 
which at least one of the specified radicals has one of the meanings which 
is indicated above as preferred. Some preferred groups of compounds can be 
expressed by the following part formulae Ia to Ig which correspond to the 
formula I and in which the unspecified radicals have the meaning indicated 
for formula I, but in which 
in Ia 
R.sup.1 is 2-, 3- or 4-pyridyl, 2- or 3-thienyl, 2- or 3-furyl, 
1-methyl-2-pyrryl, styryl, p-dimethylaminostyryl or 3,4-dimethoxystyryl; 
in Ib 
R.sup.1 is 2-, 3- or 4-pyridyl, 2- or 3-thienyl, 2- or 3-furyl, 
1-methyl-2-pyrryl, styryl, p-dimethylaminostyryl or 3,4-dimethoxystyryl, 
R.sup.2 R.sup.4 and R.sup.5 are each H or CH.sub.3, and 
R.sup.3 is H, CH.sub.3 or C.sub.2 H.sub.5 ; 
in Ic 
R.sup.1 is 2-, 3- or 4-pyridyl or 2- or 3-thienyl, 
R.sup.2, R.sup.4 and R.sup.5 are each H or CH.sub.3, and 
R.sup.3 is H, CH.sub.3 or C.sub.2 H.sub.5 ; 
in Id 
R.sup.1 is 2-, 3- or 4-pyridyl or 2- or 3-thienyl, 
R.sup.2, R.sup.4 and R.sup.5 are each H or CH.sub.3, 
R.sup.3 is H, CH.sub.3 or C.sub.2 H, and 
R.sup.6 and R.sup.7 are each H; 
in Ie 
R.sup.1 is 2-, 3- or 4-pyridyl or 2- or 3-thienyl, 
R.sup.2, R.sup.4 and R.sup.5 are each H or CH.sub.3, and 
R.sup.3 is H, CH.sub.3 or C.sub.2 H.sub.5, and 
R.sup.6 and R.sup.7 together are a C--C bond; 
in If 
R.sup.1 is 2-, 3- or 4-pyridyl, 2- or 3-thienyl, 2- or 3-furyl, 
1-methyl-2-pyrryl, styryl, p-dimethylaminostyryl or 3,4-diemthoxystyryl, 
R.sup.2 is H or CH.sub.3, 
R.sup.3 is CH.sub.3 or C.sub.2 H.sub.5, and 
R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are each H; 
in Ig 
R.sup.1 is 2-, 3- or 4-pyridyl or 2- or 3-thienyl, 
R.sup.2 is H or CH.sub.3, 
R.sup.3 is CH.sub.3 or C.sub.2 H.sub.5, and 
R.sup.4, R.sup.5, R.sup.6 and R.sup.7 are each H. 
Moreover, the compounds of the formula I are prepared by methods known per 
se and as are described in the literature (for example in the standard 
works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of 
Organic Chemistry], published by Georg Thieme, Stuttgart; but, in 
particular, in German Offenlegungsschrift No. 2,837,161), namely under 
reaction conditions which are known and suitable for the reactions 
mentioned. It is also possible to make use for this purpose of variants 
which are known per se and which are not mentioned here in detail. 
Thus, the compounds of formula I and their salts can be prepared by methods 
wherein a diamine of the formula II 
##STR3## 
in which R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6 and R.sup.7 have the 
indicated meanings, is reacted with an acid of the formula R.sup.1 --COOH 
(in which R.sup.1 has the idicated meaning) or with one of its reactive 
derivatives or with an aldehyde of the formula R.sup.1 --CHO (in which 
R.sup.1 has the indicated meaning) in the presence of an oxidizing agent, 
or a compound of the formula III, which is optionally prepared in the 
reaction mixture, 
##STR4## 
in which one of the radicals X and Y is H, 
and the other of these radicals is the group R.sup.1 --CZ.sup.1 Z.sup.2 --, 
Z.sup.1 and Z.sup.2, which can be identical or identical or different, are 
each 
OH or SH groups which are optionally substituted by alkyl, or together are 
O, S, NH, N-alkyl, alkylenedioxy or alkylenedithio, each having 2 or 3 C 
atoms, and 
R.sup.1 or R.sup.7 have the indicated meanings, 
is cyclized 
or a keto acid of the formula IV 
##STR5## 
in which R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.6 and R.sup.7 have 
the indicated meanings, or one of its reactive derivatives, is reacted 
with a hydrazine of the formula R.sup.5 --NH--NH.sub.2 (in which R.sup.5 
has the indicated meaning) or with one of its reactive derivatives, and/or 
in that a tetrahydropyridazinone of the formula I (R.sup.6 =R.sup.7 =H) is 
converted, by treatment with dehydrogenating agents, into the 
corresponding dihydropyridazinone of the formula I (R.sup.6 and R.sup.7 
together=C--C bond), and/or in that one functional group in a compound of 
the formula I is converted into another functional group, and in that, 
where appropriate, a base of the formula I is converted, by treatment with 
an acid, into one of its salts. 
The starting materials can, if desired, also be formed in situ, in such a 
manner that they are not isolated from the reaction mixture but are 
immediately reacted further to give compounds of the formula I. On the 
other hand, it is possible to carry out the reaction stepwise, it being 
possible to isolate further intermediates. 
Thus, the compounds of the formula I can be obtained by reaction of 
diamines of the formula II with acids of the formula R.sup.1 --COOH or 
their reactive derivatives. Particularly suitable reactive derivatives of 
the acids are the corresponding nitriles, acid halides, esters, amides, 
imidic esters, imidic thioesters, imidic acid halides, amidines, 
thiocarboxylic esters, dithiocarboxylic esters or ortho esters. 
Some of the starting materials of the formulae II and R.sup.1 --COOH are 
known. Those which are unknown can be prepared by methods known per se, 
for example from German Offenlegungsschrift No. 2,837,161. The carboxylic 
acids of the formula R.sup.1 --COOH can be obtained by, for example, 
oxidation of corresponding aldehydes of the formula R.sup.1 --CHO. 
In detail, the reaction of the diamines of the formula II with the acids of 
the formula R.sup.1 --COOH, or with their reactive derivatives, takes 
place in the presence or absence of an inert solvent, at temperatures 
between about -20.degree. and about 250.degree., preferably between 
60.degree. and 150.degree.. Examples of suitable solvents are hydrocarbons 
such as benzene, toluene, xylenes or mesitylene; halogenated hydrocarbons 
such as dichloromethane, trichloroethylene or chlorobenzene; tertiary 
bases such as triethylamine, pyridine or picolines; alcohols such as 
methanol, ethanol or isopropanol; glycols and glycol ethers such as 
ethylene glycol, diethylene glycol, or 2-methoxyethanol; ketones such as 
acetone; ethers such as tetrahydrofuran (THF) or dioxane; amides such as 
dimethylformamide (DMF), or sulfoxides such as dimethyl sulfoxide. 
Mixtures of these solvents are also suitable. In some cases, it is 
advisable to add catalytic amounts of an acid such as p-toluenesulfonic 
acid, or to add a dehydrating agent such as carbonyldiimidazole, 
phosphorus oxychloride, polyphosphoric acid or thionyl chloride, it also 
being possible for the dehydrating agent to act as the solvent. 
If the free carboxylic acids of the formula R.sup.1 --COOH are used, the 
reaction is preferably carried out in the presence of one of the 
dehydrating agents mentioned and, where appropriate, of a tertiary base 
such as pyridine or triethylamine, preferably at temperatures between 
-20.degree. and 150.degree.. A particularly favorable method comprises the 
reaction of the diamine with the acid in THF in the presence of 
carbonyldiimidazole at room temperature. 
The reaction can also be carried out stepwise. Thus, for example, it is 
possible partially to acylate II with an acid chloride of the formula 
R.sup.1 --COCl to give a 6-(3-R.sup.1 CO--NH-4-R.sup.2 
NH-phenyl)pyridazin-3-one or a 6-(3-amino-4-R.sup.1 CO--NR.sup.2 
-phenyl)pyridazin-3-one (or the corresponding 4,5-dihydropyridazin-3-ones; 
or to give mixtures of the isomers), which is subsequently dehydrated, for 
example by boiling with acetic acid, to give I. 
It is also possible to use, in place of the acid, a corresponding aldehyde 
of the formula R.sup.1 --CHO when an oxidizing agent is simultaneously 
present. The oxidizing agent which is preferably used is sulfur in a 
hydrocarbon such as benzene, toluene, xylene or mesitylene, or sodium 
disulfite in solvents such as dimethylacetamide, in each case at 
temperatures between about 80.degree. and about 200.degree.. The aldehdyes 
are, as a rule, known and can be obtained by, for example, formylation of 
the corresponding base compounds R.sup.1 --H, for example by the method of 
Vilsmeier-Haack. 
The compounds of the formula I can also be obtained by cyclization of 
compounds of the formula III. In the latter, the radicals Z.sup.1 and 
Z.sup.2 together are preferably 0. 
The cyclization is preferably carried out in a solvent such as ethanol, 
isopropanol, acetic acid, chlorobenzene, ethylene glycol, DMF, tetralin or 
in an excess of the acylating agent used for the preparation of the 
compound of the general formula II, for example in R.sup.1 CN, (R.sup.1 
CO).sub.2 O, R.sup.1 COOH, R.sup.1 CSOH or R.sup.1 CSSH or their esters, 
amides or halides, at elevated temperatures, for examples at temperatures 
between 0.degree. and 250.degree., where appropriate in the presence of a 
condensing agent such as phosphorus oxychloride, thionyl chloride, 
sulfuryl chloride, sulfuric acid, hydrochloric acid, phosphoric acid, 
acetic acid, acetic anhydride or, where appropriate, also in the presence 
of a base such as potassium ethylate or potassium tert.-butylate. However, 
the cylization can also be carried out without solvent and/or without 
condensing agent. 
However, the reaction is particularly advantageously carried out in such a 
manner that an appropriate 6-(acylaminonitrophenl)pyridazin-3-one is 
converted into a corresponding compound of the formula III be reduction, 
for example by reduction with hydrogen in the presence of a hydrogenation 
catalyst such as Raney nickel, platinum or palladium/charcoal, by 
reduction with metals such as iron, tin or zinc, or by reduction with 
metal salts such as iron (II) sulfate, tin (II) chloride or chromium (II) 
chloride, the compound of the formula III being cyclized, where 
appropriate in the same reaction mixture and, if necessary, in the 
presence of an acid such as hydrochloric acid, sulfuric acid, phosphoric 
acid, acetic acid or a carboxylic acid of the formula R.sup.1 COOH, or in 
the presence of a condensing agent such as phosphorus oxychloride or in 
the presence of a base such as potassium ethylate, where appropriate in a 
solvent such as ethanol, isopropanol, ethylene glycol, DMF, dimethyl 
sulfoxide or chlorobenzene, at temperatures between 0.degree. and 
250.degree.. 
The compounds of the formula I can also be obtained by reaction of a keto 
acid of the formula IV, or of one of its reactive derivatives, with a 
hydrazine of the formula R.sup.5 --NH--NH.sub.2, or one of its reactive 
derivatives. 
The carboxylic acids of the formula IV can be prepared by methods known per 
se, for example in analogy to German Offenlegungsschrift No. 2,837,161. 
Particularly suitable reactive derivatives of the carboxylic acids of the 
formula IV are the esters, for example the alkyl esters in which the alkyl 
group preferably has 1-4 C atoms, in particular the methyl and ethyl 
esters, also the nitriles, the acid halogenides, for example, acid 
chlorides or acid bromides, and the amides. Other suitable reactive 
derivatives of the carboxylic acids of the formula IV can be formed in 
situ during the reaction, without being isolated. These include, for 
example, the hydrazones of the formula Ben-C (.dbd.NNHR.sup.5)--CR.sup.3 
R.sup.6 --CR.sup.4 R.sup.7 --COOH and the hydrazides of the formula 
Ben-CO--CR.sup.3 R.sup.6 --CR.sup.4 R.sup.7 --CO--NHNHR.sup.5 (in which 
Ben is the 1-R.sup.2 -2-R.sup.1 -5-benzimidazolyl radical). 
Examples of suitable reactive derivatives of the hydrazine of the formula 
R.sup.5 --NH--NH.sub.2 are the corresponding hydrazine hydrates, acetyl 
hydrazines, semicarbazides or carbazic esters. 
For the reaction with the carboxylic acids of the formula IV, or with their 
reactive derivatives, it is advantageous to use 1-5 equivalents of the 
hydrazine, or of reactive hydrazine derivative, which can act as the 
solvent. However, it is preferable to add an additional inert solvent. 
Suitable inert solvents which are preferred are alcohols such as methanol, 
ethanol, isopropanool, n-butanol, isoamyl alcohol, glycols and their 
ethers, such as ethylene glycol, diethylene glycol, ethylene glycol 
monomethyl or monoethyl ether (methylglycol or ethylglycol), carboxylic 
acids such as formic, acetic or propionic acid, also ethers, in particular 
water-soluble ethers such as tetrahydrofuran, dioxane or ethylene glycol 
dimethyl ether (diglyme); also water and mixtures of these solvents with 
one another, in particular mixtures with water, for example aqueous 
ethanol. It is also possible to add an acid, such as sulfuric acid or 
p-toluenesulfonic acid, as a catalyst. The reaction temperatures are 
preferably between about 0.degree. and 200.degree., preferably between 
20.degree. and 100.degree., and the reaction times are between about 1 and 
48 hours. 
A tetrahydropyridazinone of the formula I (R.sup.6 =R.sup.7 =H) can, if 
desired, be dehydrogenated to give a corresponding dihydropyridazinone (I, 
R.sup.6 and R.sup.7 together are a C--C bond). Examples of suitable 
dehydrogenating agents are bromine, PCl.sub.5, sodium 
3-nitrobenzenesulfonate, CrO.sub.3, N-bromosuccinimide, H.sub.2 O.sub.2, 
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or NaNO.sub.2, in a 
solvent such as dioxane, acetic acid, propionic acid or nitrobenzene, at 
temperatures between about 0.degree. and 120.degree., preferably between 
50.degree. and 100.degree.. 
It is also possible to convert, in a manner known per se, one functional 
group in a compound of the formula I into another functional group. 
Thus, for example, OH, SH or NH groups can be alkylated to give alkoxy, 
alkylthio, monoalkylamino or dialkylamino groups, NH groups can be 
acylated to give acylamino groups, NO.sub.2 groups can be reduced to give 
NH.sub.2 groups, carboxyl groups can be esterified to give COOalkyl 
groups, or can be converted via the corresponding amides into CN groups, 
ester groups can be hydolyzed to give COOH groups, and halogen atoms can 
be converted with metal cyanides into CN groups. All these conversions are 
carried out by methods which are described in the literature (for example 
Houben-Weyl, loc. cit.) and are familiar those skilled in the art. 
A base of the formula I can be converted with an acid into the relevant 
acid addition salt. Particularly suitable acids for this reaction are 
those which provide physiologically acceptable salts. Thus, it is possible 
to use inorganic acids, for example sulfuric acid, nitric acid hydrogen 
halide acids, such as hydrochloric acid or hydrobromic acid, phosphoric 
acid, such as orthophosphoric acid, and sulfamic acid, as well as organic 
acids, in particular aliphatic, alicyclic, araliphatic, aromatic or 
heterocyclic monobasic or polybasic carboxylic, sulfonic or sulfuric 
acids, for example formic acid, acetic acid, propionic acid, pivalic acid, 
diethylacetic acid, malonic acid, succinic acid, pimelic acid, fumaric 
acid, maleic acid, lactic acid, tartaric acid, malic acid, benzoic acid, 
salicylic acid, 2- or 3-phenylpropionic acid, citric acid, gluconic acid, 
ascorbic acid, nicotinic acid, isonicotinic acid, methanesulfonic or 
ethanesulfonic acid, ethanedisulfonic acid, 2-hydroxyethanesulfonic acid, 
benzenesulfonic acid, p-toluenesulfonic acid, naphthalenemonosulfonic and 
naphthalenedisulfonic acids, and lauryl sulfuric acid. Salts with 
physiologically unacceptable acids, for example picrates, can be used to 
purify the compounds of the formula I. 
An acid of the formula I can be converted by reaction with a base into one 
of its metal or ammonium salts; particularly suitable for this are the Na, 
K, Mg, Ca and ammonium salts, also substituted ammonium salts, for example 
the dimethylammonium, diethylammonium, monoethanolammonium, 
diethanolammonium, triethanolammonium, cyclohexylammonium and 
dicyclohexylammonium salts, furthermore dibenzylethylenediammonium salts, 
or salts with N-methyl-D-glucamine or with basic amino acids, such as 
arginine or lysine. 
If desired, the free bases of the formula I can be liberated from their 
salts by treatment with strong bases, such as sodium or potassium 
hydroxide, sodium or potassium carbonate. 
Compounds of the formula I may contain one or more centers of asymmetry. In 
this case, they are usually in the racemic form. Racemates which have been 
obtained can be mechanically or chemically separated into their optical 
antipodes by methods known per se. Preferably, diastereomers are formed 
from the racemic mixture by reaction with an optically active resolving 
agent. Examples of suitable resolving agents are optically active acids, 
such as the D- and L-forms of tartaric acid, diacetyltartatic acid, 
dibenzoyltartaric acid, mandelic acid, maleic acid, lactic acid or the 
various optically active camphorsulfonic acids, such as 
.beta.-camphorsulfonic acid. 
Of course, it is also possible to obtain optically active compounds of the 
formula I by the methods described above in which the starting materials 
used are already optically active. 
The invention also relates to the use of the compounds of the formula I and 
of their physiologically acceptable salts for the preparation of 
pharmaceutical formulations, in particular by non-chemical means. For this 
purpose, they can be converted into a suitable administration form 
together with at least one solid, liquid and/or semiliquid vehicle or 
auxiliary and, where appropriate, in combination with one or more other 
active compounds. 
The invention also relates to agents, in particular pharmaceutical 
formulations, containing at least one compound of the formula I and/or one 
of its physiologically acceptably salts. 
These formulations can be used as medicaments in human or veterinary 
medicine. Suitable vehicles are organic or inorganic substances which are 
suitable for eternal (for example oral), parenteral or topical 
administration and which do not react with the new compounds, for example 
water, vegetable oils, benzyl alcohols, polyethylene glycols, glycerol 
triacetate, gelatin, carbohydrates such as lactose or starch, magnesium 
stearate, talc and vaseline. In particular, tablets, coated tablets, 
capsules, syrups, elixirs or drops are used for oral administration, 
suppositories for rectal administration, solutions, preferably oily or 
aqueous solutions, also suspensions, emulsions or implants, for parenteral 
administration, and ointments, creams or powders for topical 
administration. It is also possible to freeze-dry the new compounds and to 
use the resulting lyophilizates for the preparation of, for example, 
products for injection. The formulations indicated can be sterilized 
and/or contain auxiliaries such as lubricants, preservatives, stabilizers 
and/or wetting agents, emulsifiers, salts to affect the osmotic pressure, 
buffer substances, colorants, flavorings and/or perfumes. They can, if 
desired, also contain one or more other active compounds, for example one 
or more vitamins. 
The invention also relates to the use of the compounds of the formula I for 
controlling diseases, in particular cardiace insufficiency, and to their 
use for the therapeutic treatment of the human or animal body. 
This entails the substances according to the invention being, as a rule, 
administered in analogy to known substances having a positive inotropic 
effect, such as amrinone, preferably in doses between about 1 and 100 mg, 
in particular between 2 and 20 mg, per dosage unit. The daily dose is 
preferably between about 0.02 and 2 mg/kg of body weight. However, the 
specific dose for each particular patient depends on a very wide variety 
of factors, for example on the activity of the specific compound used, on 
the age, body weight, generaly state of health, sex, on the diet, on the 
time and route of administration, on the rate of excretion, the medicament 
combination and the severity of the particular disease to which the 
thereapy is applied. Oral administration is preferred. Compared with the 
digitalis glycosides hitherto used for the therapy of cardiac 
insufficiency, the compounds of the formula I are distinguished by an 
improved therapeutic range and peripheral relief. 
Without further elaboration, it is believed that one skilled in the art 
can, using the preceding description, utilize the present invention to its 
fullest extent. The following preferred specific embodiments are, 
therefore, to be construed as merely illustrative, and not limitative of 
the remainder of the disclosure in any way whatsoever. In the preceding 
text and the following examples, all temperatures are set forth 
uncorrected in degrees Celsius and all parts and percentages are by 
weight, unless otherwise indicated. 
In the examples which follow, "usual working up" means: if necessary, water 
or dilute sodium hydroxide solution if added, extraction is carried out 
with an organic solvent such as ethyl acetate, chloroform or 
dichloromethane, the organic phase is separated off, dried over sodium 
sulphate, filtered and evaporated, and purification by chromatography 
and/or crystallization is carried out.

EXAMPLE 1 
A mixture of 17 g of isonicotinoyl chloride, 21.8 g of 
5-methyl-6-(3,4-diaminophenyl)-4,5-dihydropyridazin-3-one ("IIa"; m.p. 
195.degree.-196.degree.) and 400 ml of chlorobenzene is boiled for 2 
hours. After having been cooled, the usual working up is carried out and, 
initially, an oily mixture of 
5-methyl-6-(3-amino-4-isonicotinamidophenyl)- and 
5-methyl-6-(3-isonicotinamido-4-aminophenyl)-4,5-dihydropyridazin-3-one is 
obtained, which is dissolved in 400 ml of acetic acid and boiled for 3 
hours. After having been cooled, 
5-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one 
("M"), dihydrate, m.p.195.degree.-198.degree. (decomposition) is obtained. 
Dihydrochloride-dihydrate, m.p. 224.degree.-227.degree.. 
Methanesulphonate, m.p. 282.degree.-285.degree.. 
The following 5-methyl-6-(2-R.sup.1 
-5-benzimidazolyl-4,5-dihydropyridazin-3-ones are obtained analogously 
using the appropriate acid chlorides: 
______________________________________ 
R.sup.1 = 
styryl, hydrochloride, decomposition above 306.degree. 
p-methylstyryl 
o-methoxystyryl 
m-methoxystyryl 
p-methoxystyryl, hydrochloride-monohydrate, 
decomposition above 306.degree. 
3,4-dimethoxystyryl, hydrochloride, decomposition 
above 285.degree. 
3,4,5-trimethoxystyryl 
p-methylthiostyryl 
o-fluorostyryl 
m-fluorostyryl 
p-fluorostyryl 
o-chlorostyryl 
R.sup.1 = 
m-chlorostyryl 
p-chlorostyryl 
p-bromostyryl 
p-iodostyryl 
p-hydroxystyryl 
p-mercaptostyryl 
p-aminostyryl 
p-methylaminostyryl 
o-dimethylaminostyryl 
m-dimethylaminostyryl 
p-dimethylaminostyryl, hemihydrate, decomposition 
above 268.degree. 
p-acetamidostyryl 
p-nitrostyryl 
p-carboxystyryl 
p-methoxycarbonylstyryl 
p-ethoxycarbonylstyryl 
p-cyanostyryl 
2-pyrryl 
1-methyl-2-pyrryl, hydrochloride, decomposition 
above 324.degree. 
2-furyl, hydrochloride, decomposition above 276.degree. 
5-methyl-2-furyl 
5-bromo-2-furyl 
5-nitro-2-furyl 
3-furyl 
2-thienyl, hydrochloride, decomposition above 316.degree. 
5-methyl-2-thienyl 
5-methoxy-2-thienyl, 
5-chloro-2-thienyl, m.p. 310-313.degree. 
4-bromo-2-thienyl, hydrochloride-monohydrate, 
m.p. 304-306.degree. 
5-bromo-2-thienyl, hydrochloride, m.p. 313-315.degree. 
5-nitro-2-thienyl 
5-cyano-2-thienyl, hydrochloride-hemihydrate, 
decomposition above 303.degree. 
3-thienyl, hydrochloride, m.p &gt; 300.degree. 
2-pyridyl, hydrochloride-monohydrate, decomposition 
above 222.degree. 
6-methyl-2-pyridyl, dihydrochloride-hemihydrate, 
decomposition above 312.degree. 
3-pyridyl, dihydrate, decomposition above 173.degree. 
R.sup.1 = 
4-chloro-3-pyridyl 
2,6-dichloro-4-pyridyl 
4-thiazolyl 
4-methyl-2-thiazolyl 
2,4-dimethyl-5-thiazolyl 
3-pyrazolyl, hydrochloride-hemihydrate, 
no m.p. up to 320.degree. 
5-methyl-3-pyrazolyl 
2-imidazolyl 
4(5)-imidazolyl 
2-methyl-4(5)-imidazolyl 
5-methyl-4-imidazolyl, dihydrochloride-monohydrate, 
no m.p. up to 320.degree. 
3-isoxazolyl 
1,2,4-triazol-5-yl 
pyrazinyl 
4-indolyl, hydrochloride-hydrate, decomposition above 338.degree. 
5-indolyl 
2-quinolyl 
4-quinolyl 
1-isoquinolyl. 
______________________________________ 
EXAMPLE 2 
A mixture of 12.3 g of isonicotinic acid, 23.2 g of 
5-methyl-6-(3-amino-4-methylaminophenyl)-4,5-dihydropyridazin-3-one, 16.2 
g of N,N'-carbonyldiimidazole and 600 ml of THF is stirred at 25.degree. 
for 16 hours. After the usual working up, an oily mixture of 
5-methyl-6-(3-amino-4-N-methylisonicotinamidophenyl)- and 
5-methyl-6-(3-isonicotinamido-4-methylaminophenyl)-4,5-dihydropyridazin-3- 
one is obtained and is dissolved in 400 ml of acetic acid. After the 
solution has been boiled for 3 hours, then cooled and submitted to the 
usual working up, 
5-methyl-6-[1-methyl-2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin- 
3-one is obtained; dihydrochloride, decomposition above 298.degree.. 
The following 5-methyl-6-(1-methyl-2-R.sup.1 
-5-benzimidazolyl)-4,5-dihydropyridazin-3-ones are obtained analogously 
using the corresponding acids: 
______________________________________ 
R.sup.1 = styryl 
p-methylstyryl 
p-methoxystyryl 
3,4-dimethoxystyryl 
p-fluorostyryl 
p-chlorostyryl 
p-dimethylaminostyryl 
2-pyrryl 
1-methyl-2-pyrryl 
2-furyl 
5-methyl-2-furyl 
3-furyl 
2-thienyl 
3-thienyl 
2-pyridyl, hydrochloride-dihydrate, 
decomposition above 245.degree. 
6-methyl-2-pyridyl 
3-pyridyl, dihydrochloride-hydrate, 
decomposition above 222.degree. 
4-chloro-3-pyridyl 
2,6-dichloro-4-pyridyl 
4-thiazolyl 
4-methyl-2-thiazolyl 
2,4-dimethyl-5-thiazolyl 
3-pyrazolyl 
5-methyl-3-pyrazolyl 
2-imidazolyl 
4(5)-imidazolyl 
2-methyl-4(5)-imidazolyl 
1,2,4-triazol-5-yl 
4-quinolyl. 
______________________________________ 
Analogously from 
5-methyl-6-(3-amino-4-ethylaminophenyl)-4,5-dihydropyridazin-3-one, there 
are obtained the corresponding 5-methyl-6-(1-ethyl-2-R.sup.1 
-5-benzimidazolyl)-4,5-dihydropyridazin-3-ones, e.g. those with 
______________________________________ 
R.sup.1 = styryl 
2-thienyl, m.p. 199-200.degree. 
2-pyridyl, m.p. 233-234.degree. 
3-pyridyl, m.p. 204-206.degree. 
4-pyridyl, m.p. 229-230.degree.. 
______________________________________ 
EXAMPLE 3 
A mixture of 10.7 g of pyridine-4-aldehyde, 21.8 g of IIa, 19 g of sodium 
disulfite (Na.sub.2 S.sub.2 O.sub.5) and 250 ml of ethanol is boiled for 6 
hours. It is evaporated, the usual working up is carried out, and "M", 
dihydrate, m.p. 195.degree.-198.degree. (decomposition), is obtained. 
5-Ethyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one 
(dihydrochloride-dihydrate, m.p. 299.degree.-302.degree.) an the following 
5-ethyl-6-(2-R.sup.1 -5-benzimidazolyl)-4,5-dihydropyridazin-3-ones are 
obtained analogously with 
5-ethyl-6-(3,4-diaminophenyl)-4,5-dihydropyridazin-3-one: 
______________________________________ 
R.sup.1 = styryl 
p-methylstyryl 
p-methoxystyryl 
3,4-dimethoxystyryl 
p-fluorostyryl 
p-chlorostyryl 
p-dimethylaminostyryl 
2-pyrryl 
1-methyl-2-pyrryl 
2-furyl 
5-methyl-2-furyl 
3-furyl 
2-thienyl 
3-thienyl 
2-pyridyl 
6-methyl-2-pyridyl 
3-pyridyl 
4-chloro-3-pyridyl 
2,6-dichloro-4-pyridyl 
4-thiazolyl 
4-methyl-2-thiazolyl 
2,4-dimethyl-5-thiazolyl 
3-pyrazolyl 
5-methyl-3-pyrazolyl 
2-imidazolyl 
4(5)-imidazolyl 
2-methyl-4(5)-imidazolyl 
1,2,4-triazol-5-yl 
4-quinolyl. 
______________________________________ 
6-[2-(4-Pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one 
(hydrochloride, m.p. &gt;320.degree.) and the following 6-(2-R.sup.1 
-5-benzimidazolyl-4,5-dihydropyridazin-3-ones are obtained analgously with 
6-(3,4-diaminophenyl)-4,5-dihydropyridazin-3-one: 
______________________________________ 
R.sup.1 = styryl 
p-methylstyryl 
p-methoxystyryl 
R.sup.1 = 3,4-dimethoxystyryl 
p-fluorostyryl 
p-chlorostyryl 
p-dimethylaminostyryl 
2-pyrryl 
1-methyl-2-pyrryl 
2-furyl 
5-methyl-2-furyl 
3-furyl 
2-thienyl 
3-thienyl 
2-pyridyl 
6-methyl-2-pyridyl 
3-pyridyl 
4-chloro-3-pyridyl 
2,6-dichloro-4-pyridyl 
4-thiazolyl 
4-methyl-2-thiazolyl 
2,4-dimethyl-5-thiazolyl 
3-pyrazolyl 
5-methyl-3-pyrazolyl 
2-imidazolyl 
4(5)-imidazolyl 
2-methyl-4(5)-imidazolyl 
1,2,4-triazol-5-yl 
4-quinolyl. 
______________________________________ 
EXAMPLE 4 
A solution of 1 g of 
5-methyl-6-(3-amino-4-isonicotinamidophenyl)-4,5-dihydropyridazin-3-one 
[obtained by reaction of methyl 3-(3-nitro-4-aminobenzoyl)butyrate with 
isonicotinoyl chloride to give methyl 
3-(3-nitro-4-isonicotinamidobenzoyl)butyrate, reaction with hydrazine 
hydrate to give 
5-methyl-6-(3-nitro-4-isonicotinamidophenyl)-4,5-dihydropyridazin-3-one 
and hydrogenation on Pd-C] in 10 ml of acetic acid is boiled for 1.5 
hours, evaporated and the usual working up is carried out. "M", dihydrate, 
m.p. 195.degree.-198.degree. (decomposition), is obtained. 
The other compounds mentioned in Examples 1-3 can be obtained analogously. 
EXAMPLE 5 
HCl gas is passed for 2 hours into a boiling suspension of 1 g of 
5-methyl-6-(3-amino-4-nicotinamidophenyl)-4,5-dihydropyridazin-3-one in 50 
ml of isopropanol. After evaporation and the usual working up, 
5-methyl-6-[2-(3-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one, 
dihydrate, decomposition above 173.degree., is obtained. 
4-Methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one is 
obtained analogously from 
4-methyl-6-(3-amino-4-isonicotinamidophenyl)-4,5-dihydropyridazin-3- one. 
EXAMPLE 6 
A mixture of 3.1 g of 
3-methyl-4-oxo-4-[2-(4-pyridyl)-5-benzimidazolyl]butyric acid [obtainable 
from 2-(4-pyridyl)benzimidazol and methylsuccinic anhydride/AlCl.sub.3 ] 
and 2 g of hydrazine hydrate in 70 ml of acetic acid is stirred at 
100.degree. for 2 hours, the usual working up is carried out, and "M", 
dihydrate, m.p. 195.degree.-198.degree. (decomposition), is obtained. 
The following are obtained analogously with the appropriate alkyl 
hydrazines: 
1,5-dimethyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one, 
dihydrochloride dihydrate, m.p. 228.degree.-235.degree.. 
1-ethyl-5-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3- 
one, dimethanesulphonate, m.p. 232.degree.-233.degree. 
1-propyl-5-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3 
-one 
1-isobutyl-5-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin 
-3-one and 
1,5-diethyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one. 
EXAMPLE 7 
A solution of 1.2 ml of bromine in 12 ml of acetic acid is added dropwise 
to a solution of 3.42 g of "M" hydrochloride in 100 ml of acetic acid at 
70.degree., with stirring. The temperature is maintained at 70.degree. for 
1 hour, and the mixture is evaporated, the usual working up is carried 
out, and 5-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]pyridazin-3-one is 
obtained. No m.p. up to 330.degree.. 
The following 5-methyl-6-(2-R.sup.1 -5-benzimidazolyl)pyridazin-3-ones are 
obtained analogously from the appropriate 4,5-dihydropyridazin-3-ones: 
______________________________________ 
R.sup.1 = styryl 
p-methylstyryl 
p-methoxystyryl 
3,4-dimethoxystyryl 
p-fluorostyryl 
p-chlorostyryl 
p-dimethylaminostyryl 
2-pyrryl 
1-methyl-2-pyrryl 
2-furyl 
5-methyl-2-furyl 
3-furyl 
2-thienyl 
3-thienyl 
2-pyridyl 
R.sup.1 = 3-pyridyl 
4-chloro-3-pyridyl 
2,6-dichloro-4-pyridyl 
4-thiazolyl 
4-methyl-2-thiazolyl 
2,4-dimethyl-5-thiazolyl 
3-pyrazolyl 
5-methyl-3-pyrazolyl 
2-imidazolyl 
4(5)-imidazolyl 
2-methyl-4(5)-imidazolyl 
1,2,4-triazol-5-yl 
4-quinolyl, 
______________________________________ 
and the corresponding 6-(2-R.sup.1 -5-benzimidazolyl)pyridazinones, their 
5-ethyl derivatives and the corresponding 5-methyl-6-(1-methyl-2-R.sup.1 
-5-benzimidazolyl)pyridazinones, as well as: 
4-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-pyridazin-3-one 
1,5-dimethyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-pyridazin-3-one and 
1,5-diethyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-pyridazin-3-one. 
EXAMPLE 8 
A mixture of 3.05 g of "M", 2.5 g of 
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 25 ml of dioxane is 
boiled under N.sub.2 for 10 hours. The mixture is evaporated, the usual 
working up is carried out, and 
5-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]pyridazin-3-one is obtained. 
EXAMPLE 9 
A solution of 1 g of 
5-methyl-6-[2-(5-nitro-2-furyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-o 
ne in 30 ml of methanol is hydrogenated to completion on 0.2 g of 5% Pd-C 
at 20.degree. and under 1 bar. The mixture is filtered, the filtrate is 
evaporated, and 
5-methyl-6-[2-(5-amino-2-furyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-o 
ne is obtained. 
EXAMPLE 10 
0.3 ml of acetyl chloride in 3 ml of chloroform is added to a solution of 
309 mg of 
5-methyl-6-[2-(5-amino-2-furyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-o 
ne and 0.2 ml of triethylamine in 10 ml of chloroform, and the mixture is 
boiled for 3 hours. The usual working up is carried out, and 
5-methyl-6-[2-(5-acetamido-2-furyl)-5-benzimidazolyl]-4,5-dihyrdopyridazin 
-3-one is obtained. 
EXAMPLE 11 
A mixture of 1 g of 
5-methyl-6-(2-p-methoxycarbonylstyryl-5-benzimidazolyl)-4,5-dihydropyridaz 
in-3-one and 60 ml of 10% sodium hydroxide solution is stirred at 
20.degree. for 12 hours. After acidification with HCl and carrying out the 
usual working up, 
5-methyl-6-(2-p-carboxystyryl-5-benzimidazolyl)-4,5-dihydropyridazin-3-one 
hydrochloride is obtained. 
EXAMPLE 12 
A mixture of 10.7 g of pyridine-4-carboxaldehyde, 21.8 g of IIa, 15.4 g of 
benzylidene-malodinitrile and 500 ml of ethanol is boiled for 3 hours. 
After the usual working up, "M" is obtained, dihydrate, m.p. 
195.degree.-198.degree. (decomposition). 
Analogously there is obtained: 
With (+)-IIa [obtainable by reaction of 
(-)-3-(4-chloro-3-nitrobenzoyl)-butyric acid with hydrazine to 
(+)-5-methyl-6-(4-chloro-3-nitrophenyl)-4,5-dihydro-pyridazin-3-one, 
conversion to 
(+)-5-methyl-6-(4-benzylamino-3-nitrophenyl)-4,5-dihydropyridazin-3-one 
with benzylamine and hydrogenation in methanolic hydrogen chloride 
solution]: (+)-"M", m.p. 216.degree.-220.degree.. Methanesulphonate, m.p. 
280.degree.-285.degree.; [.alpha.].sub.D.sup.20 +238,0.degree. (in water). 
With (-)-IIa: (-)-"M", m.p. 219.degree.-223.degree.. Methanesulphonate, 
m.p. 280.degree.-285.degree.; [.alpha.].sub.D.sup.20 -237,9.degree. (in 
water). 
The examples which follow relate to pharmaceutical formulations which 
contain compounds of the formula I or their acid addition salts: 
Example A: tablets 
A mixture of 1 kg of "M", 4 kg of lactose, 1.2 kg of potato starch, 0.2 kg 
of talc and 0.1 kg of magnesium stearate is compressed in the usual manner 
to form tablets, in such a way that each tablet contains 10 mg of active 
compound. 
Example B: coated tablets 
Tablets are compressed in analogy to Example A, and are then coated in the 
usual manner with a coating of sucrose, potato starch, talc, tragacanth 
and colorant. 
Example C: capsules 
1 kg of 
5-methyl-6-[2-(3-thienyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one 
hydrochloride is dispensed in a usual manner into hard gelatin capsules, 
so that each capsule contains 5 mg of active compound. 
Example D: ampoules 
A solution of 1 kg of 
5-methyl-6-[2-(2-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one 
hydrochloride monohydrate in 100 ml of double-distilled water is 
sterilized by filtration, dispensed into ampoules, freeze-dried under 
sterile conditions, and sterile closure is carried out Each ampoule 
contains 2 mg of active compound. 
It is possible to obtain tablets, coated tablets, capsules and ampoules 
which contain one or more of the other active compounds of the formula I 
and/or their physiologically acceptable acid addition salts analogously. 
During the investigation of the positive inotropic activity on the isolated 
papillary muscle of the guinea pig (methods in analogy to those described 
in Arzneimittelforschung, l.c.), the following compounds of formula I were 
found to be particularly active: 
5-methyl-6-[2-(4-pyridyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one, 
dihydrate 
5-methyl-6-(2-p-methoxystyryl-5-benzimidazolyl)-4,5-dihydropyridazin-3-one, 
hydrochloride, monohydrate 
5-methyl-6-[2-(3- pyrazolyl)-5-benzimidazolyl]-4,5-dihydropyridazin-3-one, 
hydrochloride, hemihydrate 
5-methyl-6-(2-p-dimethylaminostyryl-5-benzimidazolyl)-4,5-dihydropyridazin- 
3-one, hemihydrate 
5-methyl-6-(2-styryl-5-benzimidazolyl)-4,5-dihydropyridazin-3-one, 
hydrochloride. 
The preceding examples can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding examples. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of this invention, and without departing 
from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various usages and 
conditions.