Prosthetic heart valve

A bi-leaflet heart valve having an improved hinge arrangement that allows the valve to respond quickly to flow reversals and minimizes fluttering of the leaflets in the open position. A pair of leaflets are slidably and pivotally mounted in a heart valve body for movement between closed and open positions. Notches in the leaflets matingly engage complementary surfaces on pivot projections extending inward from the valve body sidewall. Downstream stops interengage with complementary surfaces on the leaflets to cushion the final opening movement and reduce wear in critical locations to improve operating characteristics.

The present invention pertains to heart valve prostheses and in particular, 
to prosthetic heart valves using pivotable valve members, including 
bi-leaflet valves. 
BACKGROUND OF THE INVENTION 
Various types of heart valve prostheses have been developed which operate 
hemodynamically as a result of the pumping action of the heart. Among the 
types of heart valves which have been developed are valves having single 
occluders which pivot along an eccentric axis to open and close the heart 
valves, such as that described in U.S. Pat. Nos. 4,011,601, 4,423,525 and 
4,425,670, and bi-leaflet heart valves, such as those described in U.S. 
Pat. Nos. 4,484,365 and 4,535,484. The above-mentioned patents illustrate 
various arrangements for pivotally connecting the valve members or 
occluders to a valve body and disclose occluders of a variety of shapes. 
However, most of these designs have never become commercial because of 
some shortcoming, and the need continues for improved prosthetic heart 
valves for permanent implantation into the human heart. 
In its open position, a prosthetic valve should provide a passageway which 
is large and which has good flow characteristics so that blood flows 
freely therethrough without adverse boundary layer separation and with a 
minimum of drag. The heart valve should be rapidly responsive to blood 
flow to quickly open during the pumping stroke of the heart and to close 
quickly when the heart relaxes to prevent substantial regurgitation of the 
blood. The opening and closing of the valve should be sufficiently soft so 
that the patient is not disturbed by the sounds produced. The heart valve 
should be made of biocompatible and thromboresistant materials, such as 
pyrolytic carbon which is preferred, and in this regard, it is important 
that all surfaces be well washed by blood to prevent stagnation which 
might lead to eventual clotting. Furthermore, the action of the valve 
should be such that it does not cause hemolysis (breaking of blood cells). 
Heart valves must be constructed to withstand countless numbers of openings 
and closings, and wear of the interacting heart valve components thus 
becomes important. Avoidance of excessive wear at the points which define 
the pivot axes of the heart valve occluders is of particular importance, 
and U.S. Pat. No. 4,443,894, issued Apr. 24, 1984, addressed this problem. 
In the bi-leaflet valve construction shown in that patent, the mounting 
arrangement was designed so that, in moving toward the closed position, 
each spherical sector which defined the pivot axis initially moved to the 
end of a dogleg slot; then, as a part of the seating of the arcuate edges 
of the leaflets against a sealing lip or seat 26, the spherical sectors 
are withdrawn slightly from the dead end position. However, not only was 
such a construction restricted to the closing movement of a pair of valve 
leaflets, but it was essentially restricted to a construction closely 
resembling that illustrated. As a result, there was felt to be a 
continuing need to improve designs to combat wear in heart valves 
utilizing various types of pivoting occluders. 
SUMMARY OF THE INVENTION 
The present invention provides heart valves, particularly valves of a 
bi-leaflet design, having the aforementioned desirable characteristics 
wherein a mounting arrangement is provided between the valve body and a 
pivoting occluder where there is sliding engagement between the pivoting 
occluder and an open-position stop that cushions the final movement of the 
occluder to thereby soften its arrival at the full-open position and, at 
the same time, break contact between the interengaging components that 
define the axis of pivotal rotation. 
This arrangement is considered to be particularly useful in combination 
with an interengaging pivot arrangement for a pair of leaflets wherein 
projections extending from the interior wall of the annular valve body are 
formed with upstream and downstream flat surfaces and wherein the leaflets 
have notches formed with correspondingly disposed flat surfaces that lie 
in juxtaposition to the projection flat surfaces in the open position. One 
result of such an arrangement is to disengage the upstream flat surfaces 
just before the leaflets reach their fully open position, thereby reducing 
wear at this point and cushioning the ultimate movement. In addition, this 
location of the stops is effective to change the stress pattern to which 
the leaflets are subjected at the instant of final closing and thereby 
alleviate the potential fatigue of the leaflets in this general region as 
a result of countless openings and closings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A heart valve, generally designated 10, of bi-leaflet construction is 
illustrated; however, it should be apparent to one of ordinary skill in 
this art that the principles of the present invention can be applied to a 
prosthetic heart valve having a single occluder. Heart valves embodying 
the present invention exhibit rapid response in both opening and closing, 
relatively small impact when the leaflets contact the valve body, and 
substantial avoidance of hemolysis or like injury to blood cells flowing 
through the valve. 
The heart valve 10 includes a generally annular valve body 12 and a pair of 
pivoting valve occluders or leaflets 14, which open and close to control 
the normal flow of blood in the downstream direction of arrows 18 (see 
FIG. 2). Blood flows through passageway 16 which is defined by a generally 
cylindrical interior surface or sidewall 20 of body 12. The cylindrical 
surface of sidewall 20 is interrupted by a pair of diametrically opposed 
flat wall sections 24. Flanking each of these flat wall sections is a pair 
of abutments 26 which act in combination with a protrusion or ledge 27 to 
stop the rotation of the leaflets when the leaflets reach fully open 
position, as illustrated in FIGS. 1 and 2. 
As best seen in FIGS. 1 through 3, and in FIGS. 11 and 12, diametrically 
opposed projections 42 extend generally perpendicularly from the flat wall 
sections 24; each projection 42 has a pair of oppositely facing lateral 
pivots 43. Each pivot 43 has three flat seating surfaces or facets 44a, 
44b and 44c, each oriented from the next adjacent facet at an angle of 
between about 110.degree. and about 130.degree., and preferably 
approximately 125.degree.. In the preferred embodiment, facet 44a is 
oriented substantially parallel to the axis of blood flow, with the other 
two facets 44b and 44c lying upstream thereof (see FIG. 11). The 
projections 42 have center sections 47 which are recessed so as to 
minimize the transverse surface area in the path of blood flow through the 
passageway 16 and inward facing surfaces 50 of the projections 42 are flat 
and generally parallel to the flat wall section 24 of the valve body. The 
three seating surfaces 44a, 44b, and 44c are perpendicular to the flat 
wall section 24 of the valve body and to the parallel flat end portion 50. 
These pivots matingly engage with notches 53 formed in the leaflets 14. 
The leaflets 14 each have an upstream or inflow surface 30 and an opposed 
downstream or outflow surface 32. The cross-sectional view of FIG. 2, 
which is taken along the leaflet centerline perpendicular to its axis of 
rotation, shows that the thickness of the leaflets varies considerably 
from one end of the leaflet to the other. This design reduces impedance of 
the leaflets to blood flow therethrough as a result of the composite 
curvature of the leaflets. As described in the U.S. Pat. Application Ser. 
No. 392,745, filed Aug. 11, 1989, the disclosure of which is incorporated 
herein by reference, the rapid response of the leaflets to reversals in 
the direction of blood flow is attributable in part to the hinge 
mechanism. 
The inflow surface 30 of each leaflet has a concave region 70 of 
two-dimensional curvature resembling a curved sheet. As used herein, a 
two-dimensional curved surface is one which is made up of a plurality of 
straight lines that extend laterally completely across the leaflet 
arranged to define a curved surface, which lines are all parallel to one 
another. In other words, planes parallel to the pivot axis will cut the 
two-dimensional inflow surface along straight lines, whereas planes 
perpendicular to the pivot axis will cut the two-dimensional inflow 
surface along a line having the same curvature regardless of whether the 
plane is the centerline plane or laterally offset therefrom. The leaflet 
inflow surfaces 30 include a convex region 72, also of generally 
two-dimensional curvature, downstream of the concave region 70. The convex 
region 72 when cut by a plane perpendicular to the pivot axis may exhibit 
a curvature resembling a paraboloid, an ellipsoid or some other smooth 
arcuate shape. Preferably, the various portions of the major leaflet 
surfaces are blended so as to have smooth transitions from one to another. 
The outflow surface 32 of each leaflet 14 includes a convex surface region 
that is preferably at least coextensive with the opposing inflow concave 
region 70 and inflow convex region 72. The leaflets have a maximum 
thickness where the convex surfaces oppose each other. Each leaflet has a 
major arcuate peripheral surface 36, which lies in juxtaposition with the 
valve body sidewall in the closed position. 
The leaflets 14 have, in addition to the major arcuate peripheral surface 
36 which is located at the trailing edge of a fully opened leaflet, a 
minor flat mating surface 38 that is located at the opposite, leading end 
of the leaflet. The flat minor surface 38 is oriented to mate or lie in 
juxtaposition with the corresponding surface of the opposing leaflet. This 
minor surface 38 is oriented at an obtuse angle with the flat section of 
the outflow surface 32 of the leaflet 14 which angle is chosen such that 
the two minor surfaces 38 abut along substantially their entire lengths 
when the valve is in the closed position. 
Referring to FIGS. 4 and 5, leaflets 14 each include a pair of opposed, 
lateral surface sections 51 which are interposed between the major arcuate 
surface 36 and the minor mating surface 38. These lateral surface sections 
51 of the leaflets are preferably flat, and the leaflets are proportioned 
so as to provide a minimal clearance 25 with the flat wall sections 24 of 
the valve body 12 (See FIG. 3) during pivoting movement of the leaflets 
14. 
As best seen in FIG. 9, extending from the outflow surface 32, adjacent 
both lateral surface sections 51, are extensions 52 which each have an 
upstream end surface 54, a bottom surface 55, and a downstream end surface 
59. The upstream end surface 54 of the extension 52 is formed at an obtuse 
angle with the flat section of the backflow surface 32 of the leaflet 14 
so as to preferably form a continuous, smooth surface with the flat minor 
mating surface 38. The opposed minor mating surfaces 38 and the extensions 
52 provide combined surfaces of substantial thickness which result in 
several advantages on valve closing. For example, the increased surface 
area of the mating surfaces 38 distributes forces over a greater area upon 
contact between mating surfaces, thus reducing stress and wear on the 
leaflets. Also, with the valve in a fully closed position, the increased 
surface area lengthens the region of abutment between the leaflet mating 
surfaces and deters leakage. 
Notches 53 are formed in each extension 52 and have two flat or straight 
surfaces 56 and 57 oriented so as to mate with the facets 44a and 44b, 
e.g., at an angle of about 125.degree. with respect to each other, and a 
third, curved surface 58. In the preferred embodiment, the first straight 
surface 57 is substantially parallel and preferably coplanar with the flat 
section of the inflow surface 32 of the leaflet; the second straight 
surface 56 is adjacent and on the upstream side thereof (with the leaflet 
in the open position). The curved surface 58 is adjacent and on the 
downstream side of the first straight portion 57, and it extends smoothly 
therefrom, being preferably tangential thereto. The downstream surfaces 59 
of the extensions 52 are oblique in an upstream direction to the flat 
outflow section of the leaflet 14 being formed at an angle between about 
100.degree. and about 120.degree.; they are accordingly at an angle of 
between about 60.degree. and about 80.degree. to the centerline plane 
through the valve body. By the centerline plane is meant the plane which 
is perpendicular to the flat wall sections 24 and contains the centerline 
through the valve passageway. 
Referring to FIG. 2, the extensions 52 provide additional structural 
support to the upstream or leading end, otherwise flat, portions 60 of the 
leaflets 14 which carry the stress of halting leaflet movement, 
particularly in the open position. As described in U.S. Pat. Application 
Ser. No. 4,872,875, the flat leading end portions 60 of the leaflets 14, 
in the central regions between the extensions 52, have a significantly 
constant thickness, which is generally significantly less than the 
downstream thickness, as is apparent from the cross-sectional views of 
FIGS. 2 and 10. Extensions 52 are preferably formed integral with the 
leaflets 14 so that the leaflets have an increased thickness at the 
locations where stresses are encountered. 
The leaflets 14 are installed in the valve body 12 by squeezing the body at 
diametrically opposed locations, i.e. those where the valve body is cut by 
the reference line 2--2 in FIG. 1. This causes the body to bulge outward 
at the diametrically opposed flat wall sections 24, thus allowing the 
leaflets 14 to be fitted into the passageway 16 of the valve body. The 
extensions 52 of the leaflets fit between the pivots 43 and the abutments 
26, with the pivots 43 being received in the notches 53. The squeezing 
force is then removed allowing the flat wall sections 24 to return to 
their original spacing. Referring to FIG. 3, the lateral surfaces 51 and 
extensions 52 of the leaflets 14 are preferably dimensioned to provide a 
small clearance 25 with the corresponding adjacent flat wall sections 24 
of valve body 12. The notches 53 and the pivots 43 define the pivot axes 
about which the leaflets slidably and pivotally rotate between open and 
closed positions. This is discussed further below in relation to the 
operation of the valve. 
The leaflets are slidably and pivotally mounted for rotation between closed 
and open positions, and it is generally preferred that the opening, and 
particularly the closing, motions of the leaflets be made as rapid as 
possible. However, the end points of the termination of movement of the 
leaflets should be well defined and designed to reduce noise and leaflet 
wear. For example, the leaflets should not bounce back when contacting 
seating surfaces defining the end points of their travel, nor should the 
major peripheral surfaces 36 extend beyond the valve body 12 when in a 
closed position. 
FIG. 2 shows the inflow surfaces 30 of leaflets 14 lying generally adjacent 
the relatively flat, vertically oriented surfaces of the abutments 26 
which, along with downstream stops 27, define the extent of opening of the 
leaflets, thus fixing one end of their travel. The stops 27 extend 
inwardly from the flat wall sections 24 at locations downstream of the 
pivot projections; they are positioned so as to engage the oblique surface 
59 of the extensions as explained hereinafter. Similar to the pivot 
projections, the centers of the stops 27 are preferably recessed to 
minimize the transverse surface area exposed to, and impeding, the flow of 
blood through the passageway 16. Employing stops 27 in addition to 
abutments 26 to halt rotation of the leaflets 14 results in less wear on 
the pivots and the interengaging surfaces of the notches because of the 
manner in which leaflet impact 15 is cushioned at the end point of such 
movement, as explained hereinafter. On the other hand, the final closed 
position of the leaflets is defined by the abutting, minor, mating 
surfaces 38 of the leaflets, and/or the contact between the major, arcuate 
surfaces 36 and the interior surface or sidewall 20 of the valve body 12 
(which may have formed therein a seating region), and contact along the 
inclined surface of the abutment 26, likely at edge P (FIG. 10). 
As best seen in FIG. 2, abutments 26 and stops 27, in combination with the 
flat seating surfaces 44a and 44b of the pivots 43, define the fully open 
position of leaflets 14. In the preferred embodiment, the mating flat 
surfaces 38 do not extend beyond the valve body when the leaflets are in 
their open position. It is generally desirable to orient the fully open 
leaflets for minimum obstruction of the downstream flow through the valve 
body passageway 16. As can be seen in FIG. 2, the flat portions 60 of the 
leaflets 14 are oriented essentially parallel to the direction of blood 
flow, generally indicated by arrows 18. 
The leaflets 14 undergo controlled angular displacement between their fully 
closed and fully open positions. With reference to FIG. 2, the angle of 
opening (i.e. the angular orientation of the leaflets when in the open 
position), identified by the reference letter a, has a value ranging 
between about 1 and about 20.degree.. Preferably, this angle of opening of 
the leaflets is between about 5.degree. and about 20.degree., and most 
preferably, is between about 7.degree. and about 13.degree.. As used 
herein, the term "angle of opening" is defined as the angle between two 
planes which are both perpendicular to the flat surfaces 24, one of which 
(see reference character M) longitudinally bisects the minor mating 
surface 38 and also contains the midpoint of the major arcuate surface 36 
and the other of which contains the centerline of the valve body 
passageway (see reference character L). 
The centerline L of the passageway 16 through the valve body 10 lies midway 
between the pivot axes, and in the fully open position, the outflow 
surfaces 32 of the leaflets lie facing each other on opposite sides of the 
centerline L, with the portions of the leaflets 14 within the valve body 
12 extending generally parallel to the central axis L. In the fully closed 
position as shown in FIG. 10, the minor, mating surfaces 38 of the 
leaflets 14 abut each other, preferably along their entire flat surfaces. 
No matter which opening angle a is chosen, it is generally preferred that 
the leaflets 14 are not brought into a generally straight-line 
relationship when fully closed, in order to avoid a risk of wedging of the 
leaflets. Instead, the leaflets 14 should have an obtuse angular relation 
to each other, preferably less than about 150.degree., as shown in FIG. 
10. 
Operation of the heart valve 10 will now be described as the leaflets begin 
movement from a fully closed position wherein the two flat surfaces 56 and 
57 of each notch 53 lie in juxtaposition to the two upstream flat seating 
surfaces 44b and 44c of the pivot 43, there being a small clearance 
between these adjacent surfaces (see FIG. 10). When the cardiac cycle 
reverses, blood flows in the direction of the arrows 18 (FIG. 2), and in 
initial valve opening movement, the leaflets are displaced in the 
downstream direction until the flat surfaces 56 and 57 of the leaflet 
notches 53 are pressed against the facets 44b and 44c of the pivot 
projections 42. The eccentric location of the pivot axis causes a moment 
imbalance to develop as a result of the forces bearing against the larger 
portions of the inflow surfaces 30 that are located generally downstream 
of the pivot axes. This imbalance causes the leaflets 14 to begin to 
rotate about the pivots 43 in the direction of valve opening, with their 
minor mating surfaces 38 moving apart and approaching the abutments 26; 
contact is between the leaflet notch surfaces 56 and 57 and the pivots 43. 
The amount of force on the pivots 43 decreases as the leaflets 14 open 
more widely, due to reduced leaflet surface area generally transverse to 
the path of the blood flow. As the leaflets 14 swing toward the fully open 
position, the points of contact continuously change between the pivoting 
notches 53 with the edges B and C of the pivots 43, the effect of which 
continuous shifting of contact points is discussed in the aforementioned 
application. 
As shown in FIG. 11, the relative proportioning of the notches 53 and the 
relative spacing between the pivots 43 and the downstream stops 27 which 
protrude from the interior sidewall of the valve body are such that, as 
the leaflets approach the fully opened position, there is engagement 
between the upstream edge D of the stop 27 and the oblique surface 59 of 
the extension 52. The contact has two effects. First, it cushions the 
impact between the pivoting leaflet 14 and the downstream stop 27. Second, 
it effects this cushioning by forcing or lifting the leaflets slightly 
upstream, breaking contact between the edge C and the surface 56 of the 
notch, and thus alleviating a point of potential wear. The lifting results 
in a sliding of the flat notch surface 57 generally along the edge B of 
the facet 44a. As a result, as can be seen in FIG. 12, when the leaflets 
reach the fully open position, the facet 44b is in close juxtaposition to 
the notch surface 56, but there is no contact therebetween. There is, 
however, contact between the facet 44a and the notch surface 57 and 
between the oblique surface 59, near its end, and the edge D of the 
downstream stop 27, all of which serve to eliminate flutter of the 
leaflets in the open position. In addition, in the fully open position, 
there may be contact between the flat section of the inflow surface 30 of 
the leaflet and the surface of the abutment 26 that lies parallel to the 
centerline of the valve, although there can be a slight clearance between 
the two surfaces, as shown in FIG. 12. The only flutter possible in this 
open position would be extremely slight movement for a distance equal the 
extent of this tolerance, and it can thus be seen that the upstream 
abutment 26 and the downstream stop 27 in combination with this notch 
arrangement create an extremely stable open position for this bi-leaflet 
valve. 
Upon a reversal of the cardiac cycle, blood flow develops in an upstream 
direction, generally opposite that of the arrows 18 of FIG. 2. The force 
of back-flowing blood against the leaflet outflow surface 32 causes the 
leaflets 14 to be shifted slightly upstream, i.e. in an upward direction 
as depicted in FIG. 2, and to begin to pivot in a closing direction. Upon 
this shifting of each leaflet, there is engagement between the downstream 
edge labeled A on the pivot 43 and the curved notch surface 58, and there 
is contact between the lower edge P of the abutment 26 and the flat 
section of the inflow surface 30. This acts to provide an initial, rapid 
pivoting of the leaflet 14 in a closing direction which, in turn, exposes 
a greater portion of the outflow surface 32 of the leaflet to the direct 
force of the backflowing bloodstream. As the leaflet outflow surface 32 
become more transverse to the flow of blood, the rate of closing 
increases. 
The closing movement of the leaflets is stopped upon contact between the 
minor, mating edge surfaces 38 of the leaflets and/or contact of the 
major, arcuate surfaces 36 with the interior surface or sidewall 20 of the 
valve body 12 which may optionally have a seating region formed therein. 
Throughout much of the leaflet closing movement, there is contact between 
the inflow surface 30 and the edge P on abutment 26, and the leaflets come 
to rest in the fully closed position (FIG. 10) with the edge P on abutment 
26 in contact with the inflow surface 30. 
As explained in U.S. Pat. Application Ser. No. 392,745, filed Aug. 11, 
1989, at the beginning of leaflet closing movement, a large closing moment 
is favored which causes the leaflet to respond quickly to flow reversal. 
However, as the closing movement continues, the instantaneous center (IC) 
of points on the leaflet varies because of the changing points of contact 
between the notches 53 and pivots 43, the result of which is a reduced 
impact when the leaflet arcuate surface 36 contacts the valve sidewall, 
compared to the impact a similar valve member would have rotating on a 
pivot of circular cross-section. Moreover, the contact with the edge P 
during closing creates frictional drag along the flat section of the 
inflow surface 30 which slides therealong and also reduces the impact of 
closing. A result of this soft closure from the effect of the changing IC 
and the fractional drag is a significant lessening in the "water hammer" 
effect that is thought to cause cavitation which can be damaging to 
pyrolytic carbon, a preferred material of construction of heart valve 
components. Likewise, during the initial opening movement of the leaflet 
14, a large opening moment is favored which causes the leaflet to respond 
quickly to flow reversal. As the opening movement continues, the IC 
migrates so as to also tend to reduce impact which is further cushioned by 
the engagement between the oblique surface 59 and the edge D. 
Heart valves 10 constructed according to the principles set forth herein 
provide numerous advantages, particularly from the standpoint of providing 
a commercially feasible embodiment that responds very quickly to the 
reversal of flow, yet does not unduly stress the relatively thin leaflets 
at the moment of impact either at the end of the opening movement or at 
the end of the closing movement where the propensity of creating a "water 
hammer" effect is greatly reduced along with the chance of cavitation 
erosion. This is considered quite important because of the countless 
openings and closings to which a heart valve will necessarily be exposed 
over the lifetime of the recipient, and particularly by being able to 
transfer the point of potential wear to locations, namely the oblique 
surface 59 and the edge D of the downstream stop, that are not critical to 
determining pivotal movement, minor amounts of wear can be tolerated 
without adversely affecting the performance of the valve. 
Although the effects and advantages set forth in the foregoing paragraph 
are particularly true of heart valves having the leaflet construction 
shown in FIGS. 1-12, substantially all of these advantages can also be 
obtained through the use of leaflets of simpler design, such as those 
shown in the alternative embodiment of a heart valve 10' illustrated in 
FIGS. 13-15. The alternative embodiment utilizes a valve body 12' of 
precisely the same construction as that described in respect of the valve 
10 illustrated in FIGS. 1-12, in combination with a pair of leaflets 14'. 
When viewed looking at their downstream surfaces 32', the leaflets 14' 
appear identical to the leaflets 14 shown in FIGS. 1-12, but from a side 
sectional view, it is apparent that the leaflets 14' are of uniform 
thickness throughout with the exception of the regions where the pivot 
extensions 52' are located. In this respect, it can be seen that the 
downstream portion of each inflow surface 30' is concave and has the same 
curvature as the opposite convex section of the outflow surface 32'. 
Accordingly, the length and outline of the major peripheral surface 36' is 
the same as that hereinbefore described. Likewise, the flat minor mating 
surfaces 38' are also precisely the same as hereinbefore described. 
Overall, the flat sections 60' of the leaflets 14' are essentially the same 
as their counterparts in the leaflets 14 with the differences being in the 
downstream curved portions. The extensions 52' each include a notch 53' of 
precisely the same construction as earlier described, and the downstream 
oblique surface 59' of each extension, as previously described, will 
during the final segment of the opening movement engage the edge D of the 
downstream stops 27'. As a result, the cushioning effect upon the leaflets 
at the end point of their opening movement occurs as hereinbefore 
described. More specifically, as the leaflets 14' approach their fully 
open position, there is engagement between the upstream edge D of the stop 
27' and the oblique surface 59' which cushions the impact at the end point 
of the movement by forcing or lifting the leaflets slightly upstream and 
thereby breaking contact between the edge C and the surface 56' of the 
notch in the same manner as hereinbefore illustrated in respect of FIG. 
12. As a result, the simplified version of the heart valve 10' achieves 
substantially all of the advantages of the heart valve 10 while it is 
considerably easier to manufacture because of its substantially uniform 
thickness and substantially uniform curvature throughout major portions of 
the leaflets 14'. 
Although the present application sets forth the preferred embodiments which 
constitute the best mode for carrying out the invention, it should be 
understood that changes and modifications as would be obvious to one 
having the ordinary skill in this art may be made without departing from 
the scope of the invention which is defined in the claims appended hereto. 
For example, although preferably the cushioning is effected by engagement 
between an oblique surface on the leaflet and an edge of the stop, these 
could be reversed and edges on the leaflets could be positioned to engage 
oblique surfaces on the downstream stop. Although the valve body and the 
leaflets are preferably made of pyrolytic carbon or of isotropic graphite 
coated with pyrolytic carbon, which provides nonthrombogenic surface 
characteristics, other suitable materials can be employed to achieve the 
same mechanical advantages as set forth herein. Moreover, as indicated 
hereinbefore, although the preferred embodiment employs a pair of 
leaflets, the principles of the invention can be incorporated into known 
heart valves which utilize a single occluder and a downstream stop 
mechanism of this type. 
Particular features of the invention are emphasized in the claims that 
follow.