Abstract:
A prosthetic heart valve is provided that includes a ring structure that incorporates integrally a bearing block, a separate bearing block having two pins for accurate location that seats in a window in the ring structure and that is held in place by a circlip, and a pair of leaflets that are disposed in the passageway of the ring structure. The valve utilizes pyrolytic carbon in the ring structure, separate bearing block and leaflets. The valve has a simple structure, is durable and reliable, and is assembled without flexure or distortion of the ring structure, separate bearing block or leaflets.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to prosthetic heart valves, more particularly to prosthetic heart valves made with pyrolytic carbon.  
       BACKGROUND OF THE INVENTION  
       [0002]     The main function of a prosthetic heart valve is to provide unidirectional, uniform and reliable flow of blood in the human circulatory system. Additionally, such a valve should be comprised of materials that are compatible with body tissues when implanted and should be capable of long duty life.  
         [0003]     Prosthetic heart valves having two leaflets, also identified as bi-leaflet or double leaflet heart valve prostheses, are known in the prior art. Such a structure typically incorporates an annular member, also identified as a ring member, and two cooperating leaflets that are intended to open and close the passageway through the ring member responsive to blood flow.  
         [0004]     Because pyrolytic carbon appears to be compatible with human body tissues and to be suitable for implantation for extended time periods, and also to have desirable characteristics and features, such as great hardness, low friction, high durability, wear resistance, and deterioration resistance, it would perhaps be useful in prosthetic heart valves. Pyrolytic carbon, methods for coating substrate bodies with pyrolytic carbon, and methods for fabricating pyrolytic carbon structures are well known (see, for example, Bokros et al. U.S. Pat. Nos. 3,298,921; 3,399,969; 3,526,005 and 3,547,676).  
         [0005]     However, attempts to employ pyrolytic carbon in bi-leaflet prosthetic heart valves have presented problems. For example, assembly of preformed and pyrolytic carbon coated leaflets with a preformed and pyrolytic carbon coated ring structure was not successful because of the characteristically rigid and relatively inflexible nature of pyrolytic carbon. The engagement of the ears of the leaflets with recesses defined in the ring member involved flexing which injured the pyrolytic carbon coating and deleteriously affected the subsequent use life and usability of the prosthesis especially between adjacent bearing surfaces even when only minimal contact occurred therebetween.  
         [0006]     A little component flexing during prosthesis assembly is sometimes achievable either by providing two arm-like projections on the ring member that are preferably flat and by using leaflets that are adapted for engaging recesses provided on either the blood inlet or the outlet side of the ring member. The projections need to be thin in cross-section so as to make them slightly more flexible than otherwise. However, the undesirable possibilities of producing residual permanent deformation of the ring member or of cracking the ring member during the prosthesis assembly process cannot be completely eliminated. Also, with such thin structural members, the resulting minimum bearing engagement between adjacent surfaces makes the ears of each leaflet prone to slipping or dislodgement from their associated recesses in the resulting prosthesis after implantation and during use. Further, using flat, arm-like projections on the ring member can make the ring member very cumbersome, risky to handle and utilize, and can require careful extra efforts to insert the resulting heart valve prosthesis into an appropriate position in the patient&#39;s heart, particularly during an aortic valve replacement operation.  
         [0007]     The alternative of a thin cross-section for the ring member hardly provides the required minimum rigidity for a ring member. If such a ring member is used, the resulting heart valve prosthesis is an intrinsically weak device. The unitary construction of the ring member with its bearing surface defining recesses to accommodate the ears of the leaflets results in an inherent inability to adjust axial play precisely in the hinging mechanism, such as is necessary to minimize malfunction, disruption and consequent dislodgement of the leaflets over a period of time in use.  
         [0008]     Thus, the provision of providing either flat arm projections on the ring member, or a thin cross-section in the ring member, together with achieving the minimum bearing surface engagement needed between ears and recesses, and the inability to adjust or accurately control axial end-play in the hinging mechanism, limits long term reliable service of the presently available prior art bi-leaflet heart valve prostheses.  
         [0009]     Since safety of human life is involved, improved structure and fabrication processes are needed to achieve efficient and reliable service of bi-leaflet heart valve prostheses fabricated with pyrolytic carbon. Even a very low failure rate for heart valve prostheses is undesirable.  
         [0010]     Moreover, an improved pyrolytic carbon-containing, bi-leaflet heart valve prosthesis should achieve optimal expected long service life characteristics.  
         [0011]     There is a need for a new and improved heart valve prosthesis of the bi-leaflet type which utilizes pyrolytic carbon and which surpasses the performance and improves the reliability of prior art heart valve prostheses. The present invention provides such an improved heart valve prosthesis.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention relates to an improved prosthetic heart valve of the bi-leaflet type which incorporates pyrolytic carbon and which achieves improved reliability and durability, easy assembly, long use life, and also improved ease and reduction of cost in manufacture and assembly.  
         [0013]     The inventive heart valve prosthesis incorporates an annular or ring-like structure in which a bearing block receiving window is provided. In the window, a bearing block is demountably received and reliably retained by means of a preferably cross-sectionally circular circlip that associates with groove means in the annular structure. The bearing block has a taper about its perimeter which cooperatingly associates with a corresponding mating taper defined about the periphery of the window, and preferably these components are generally rectangularly configured. An integrally formed portion of the annular structure that is located diametrically opposite the receiving window and the associated bearing block is adapted to function as the needed second bearing block. These respective bearing blocks each have two recesses defined therein.  
         [0014]     The leaflets of the prosthesis are disposed in and across the passageway in the annular structure, and each leaflet has a pair of projecting ears that in the assembled prosthesis each cooperate and associate with a different recess defined in the combination of annular structure with associated separate bearing block, thereby to receive and support the ears so that the leaflets are adapted for achieving precise pivotable movements in the passageway to provide valve-defining operation without the possibility of leaflet slippage.  
         [0015]     During prosthesis assembly, and the associating of the leaflets with the annular structure and the separate bearing block, the separate bearing block is loosened relative to the annular structure. Assembly is achieved without flexure or bending of components (except for the circlip).  
         [0016]     Except for the circlip, and optional but preferable locating pins employed for precisely positioning the separate block in the block receiving window, the components are comprised of pyrolytic carbon. The retaining circlip for the separate bearing block relative to the annular structure is comprised of a rust-proof spring steel and the locating pins are preferably comprised of rust-proof steel.  
         [0017]     The product prosthesis is comprised of a minimum number of components and is a relatively simple structure of great durability that is human body compatible when implanted.  
         [0018]     The prosthesis components can be separately and accurately fabricated with conventional processing including use of machine tools.  
         [0019]     Assembly of the components is simple and reliable. No flexing, bending, or the like of components utilizing pyrolytic carbon is involved.  
         [0020]     The product prosthesis is very reliable, provides excellent service for an extended time period, and is very efficient.  
         [0021]     The pair of pivotable leaflets employed in the prosthesis combination functions to achieve a one-way valve and to control unidirectional blood flow through the passageway of the annular member. In the valve closed position, the edge portions of each leaflets are preferably configured to abut and engage sealingly with and against adjacent surface portions contacted therewith. Each leaflet is preferably flattened and its perimeter includes an arcuately extending outside edge region, a straight inside edge region, and a pair of flattened, ear-like projections, each one of which is located between a different pair of the adjacent opposite sides that extend between each end of the arcuate edge region and of the straight edge region.  
         [0022]     Out-turned flanges at opposite ends of the annular member provide rigidity and strength. The bearing recesses achieved in each of the bearing blocks can be precisely located and sized.  
         [0023]     Small, uniform clearances between respective adjacent portions of the leaflet ears and the bearing recesses are achieved by the precise interrelationship between components, such as that between the annular structure and the associated bearing blocks. Free, smooth, self-aligning spherical bearing surfaces are achieved for pivotal hinging-type movements of the leaflets relative to the bearing blocks. End play is adjusted by selective assembly and by precise construction, as those skilled in the art will readily appreciate.  
         [0024]     The leaflet ears engage their associated bearing recesses to a desired, predetermined depth. Each of the leaflets is held securely while achieving a minute gap between each leaflet&#39;s ears and its associated bearing housing so that there is no possibility of malfunction.  
         [0025]     The provision of pyrolytic carbon particularly in the regions of the bearing surfaces between the respective ears and the associated recesses, and the configuration of the bearing surfaces thus provided, ensures that the leaflet ears do not disengage or slip from bearings in the assembled prosthesis. The pyrolytic carbon in such regions provides a polished and hard surface.  
         [0026]     Other and further features, purposes, objects, aims, advantages, embodiments and the like will be apparent to those skilled in the art from the present description taken with the appended drawings and the following claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     In the drawings:  
         [0028]      FIG. 1  is an isometric view of one embodiment of the inventive prosthetic bi-leaflet heart valve showing each leaflet in closed position;  
         [0029]      FIG. 2  is a plan view of the valve of  FIG. 1 , with some parts thereof being shown in transverse section, this view being taken along the line II-II of  FIG. 1 ;  
         [0030]      FIG. 2A  is a fragmentary, enlarged view showing a region of the perimeter edge portion of the bearing block receiving window that is defined in the medial side wall portion of the annular ring-like structure, portions thereof being broken away and portions thereof being shown in section, this view being taken from an interior region of the ring-like structure looking outwardly at the window perimeter edge region;  
         [0031]      FIG. 3  is an isometric view similar to  FIG. 1  but showing the valve in an exploded format;  
         [0032]      FIG. 4  is a longitudinal sectional view taken along the axis of the  FIG. 1  valve as indicated by the line IV-IV in  FIG. 1 , this view being taken through the pivot axes of the leaflets;  
         [0033]      FIG. 5  is a longitudinal sectional view through the ring structure taken along the line V-V of  FIG. 2 ;  
         [0034]      FIG. 5A  is a fragmentary longitudinal sectional view taken along the line VA-VA of  FIG. 2 ;  
         [0035]      FIG. 6  is a plan view of the circlip employed in the valve of  FIG. 1 ;  
         [0036]      FIG. 7  is a plan view of the inside face of the bearing block employed in the valve of  FIG. 1  showing the bearing recesses defined therein;  
         [0037]      FIG. 8  is a longitudinal vertical sectional view through the  FIG. 7  bearing block taken along the line VIII-VIII of  FIG. 7 ;  
         [0038]      FIG. 9  is a fragmentary vertical sectional view through the  FIG. 7  bearing block taken along the line IX-IX of  FIG. 7 ;  
         [0039]      FIG. 10  is a plan view of the upper face of the right-hand leaflet employed in the valve of  FIGS. 1-4 ;  
         [0040]      FIG. 11  is a fragmentary vertical sectional view through the  FIG. 10  leaflet taken along the line XI-XI of  FIG. 10 ;  
         [0041]      FIG. 12  is a fragmentary enlarged detail view similar to a portion of  FIG. 4  illustrating pivoting movements of the  FIG. 10  leaflet relative of the separate bearing block in the valve of  FIG. 1  with one position of the leaflet being shown in phantom;  
         [0042]      FIG. 12A  is a view similar to  FIG. 12  but rotated 180° to illustrate the interior face of the integral bearing block and pivoting movements of the  FIG. 10  leaflet relative to the integral bearing block;  
         [0043]      FIG. 13  is a fragmentary, enlarged, detail, transverse sectional view through the region of the bearing block in the valve of  FIG. 1  taken along the line XIII-XIII of  FIG. 4 ;  
         [0044]      FIG. 14  is a fragmentary, enlarged, detail, exterior side elevational view at the region of the bearing block in the valve of  FIG. 1 ;  
         [0045]      FIG. 15  is a view similar to  FIG. 14  but showing an alternative embodiment that employs two circlips for retaining the bearing block in association with the ring structure; and  
         [0046]      FIG. 16  is a fragmentary, enlarged, detail, transverse sectional view through the region of the bearing block of the alternative embodiment of  FIG. 15 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0047]     The inventive heart valve prosthesis is described and illustrated with reference to a particular now preferred embodiment  21  as shown in  FIGS. 1 through 14 , respectively. The prosthesis embodiment  21  includes in combination as cooperating components an annular ring-like structure  30 , two valve leaflets  31  and  32 , a bearing block  33 , and a retaining ring or circlip  34 . Except for the circlip  34 , which is comprised of a non-rusting, resilient, spring steel, such as stainless steel or the like, and the optional but preferred locating pins  23 ,  24  which are preferably comprised of a non-rusting steel, all the components of the prosthesis  21  are comprised of pyrolytic carbon.  
         [0048]     The pyrolytic carbon components are characterized by hard, highly polished, smooth, and glossy surface portions and capacity for long wear and resistance to wear with minimal frictional losses.  
         [0049]     The ring structure  30  has a longitudinal axis  40  (shown, for example, in  FIG. 4 ) and is generally annularly configured. Also, ring structure  30  preferably is somewhat axially elongated (relative to axis  40 ), with medial generally cylindrical sidewall portions  46  and with opposite end regions  41  and  42  that extend circumferentially in generally spaced, parallel relationship relative to each other. A central passageway  43  that is generally cross-sectionally cylindrical is defined through the ring  30  about the axis  40 . Except for the bearing blocks  47 ,  33 , exteriorly, the ring structure  30  is generally cross-sectionally cylindrical. The opposite end regions  41  and  42  are each provided with an integral, outwardly extending, terminal rim flange  44  and  45 , respectively.  
         [0050]     One location along the medial sidewall portions  46  is radially selectively thickened to provide an integrally formed bearing block region  47 . The bearing block region  47  has a flat interior face  48  that extends chord-like (when the ring  30  is viewed axially) across the bearing block region  47  and parallel to the longitudinal axis  40 . Relative to the face  48 , the integral bearing block region  47  preferably has a generally rectangular perimeter configuration.  
         [0051]     A second location along the sidewall portions  46  that is generally diametrically opposed to such one location (and to the integral bearing block region  47 ) has defined therethrough a bearing block receiving window  49  (see, for example,  FIG. 3 ). Perimeter edge portions generally designated  51  of the window  49  are preferably radially thickened and include edge surface portions  52  (see, for example,  FIG. 2  or  FIG. 13 ) that are radially inclined (or beveled) and flattened to define a taper of the Morse-type or the like. The window  49  preferably has a generally rectangular perimeter configuration.  
         [0052]     A separate, or independent, bearing block  33  is provided that has perimeter edge surface portions  54  that are inclined (or beveled) and flattened to defined a peripheral taper of the Morse-type or the like. The beveled perimeter edge surface portions  54  of block  33  are configured to matingly engage with and seat against the correspondingly matingly beveled edge surface portions  52  of the window  49  when the block  33  is initially suitably oriented and aligned relative to the ring  30  with the block  33  being initially (that is, before insertion into the window  49 ) spatially oriented and positioned at an adjacent exterior location relative to the ring  30 . From such a location, the block  33  is radially (relative to the ring  30 ) moved into engagement with the window  49 . The block  33  preferably has a rectangular perimeter configuration. Alternative geometric perimeter configurations may be employed if desired for the respective perimeter portions  54  and  51 / 52 .  
         [0053]     The block  33  has a flat interior face  55  that extends chord-like (when, in the assembled prosthesis  21 , the ring  30  is viewed axially) across the bearing block  33 . The exterior face  56  of the block  33  can be variously configured, but preferably has a flattened mid-region  36  that extends parallel to the interior face  55 . Opposite side regions  37  on either side of mid-region  36  of exterior face  56  of block  33  are preferably each flattened and oriented symmetrically relative to each other and preferably each side region  37  terminates near to the adjacent exterior surface portions of the medial side wall portions  46  of the ring  30 . When the block  33  is fully seated in the window  49 , the interior face  55  extends parallel to the longitudinal axis  40 , and the faces  55  and  48  are in spaced, parallel relationship relative to each other.  
         [0054]     Preferably, as an aid to positioning a block  33  relative to a window  49 , each opposite side of edge portion  54  of the block  33  is provided with a locating pin  23 ,  24  (see, for example,  FIG. 3 ). Each pin  23 ,  24  is somewhat offset longitudinally relative to the other pin  23 ,  24  in a block  33  so as to enhance the specificity of the locating of the block  33  relative to the window  49 . Correspondingly, each opposite side region of the edge surface portions  52  of window  49  has defined therein a locating pin receiving pocket  26  (see, for example,  FIG. 2A ), each pocket  26  being somewhat offset longitudinally relative to the other pocket  26  in a window  49 . The respective locations of the pockets  26  are such that the pockets  26  are each positioned and configured to receive a different respective pin  23 ,  24  when a block  33  is seated in a window  49 . Preferably, each pin  23 ,  24  is comprised of non-rusting steel that is, during fabrication, inset into its respective location in an edge surface portion  54  of block  33 .  
         [0055]     For purposes of mounting the block  33  in position in the window  49 , the edge surface portions  51  of the window  49  in ring  30  have defined therein a perimetrically extending groove means that is achieved by a groove  57 A that extends parallel to the rim flange  44  and by another groove  57 B that extends parallel to the rim flange  45  (see, for example,  FIG. 14 ). Various arrangements and configurations can be utilized for the groove means. In general, the groove means is preferably located so as to be adjacent to outer edge portions of the exterior face  56  of the separate bearing block  33  when the block  33  is seated, as above indicated, in the window  48 . With the block  33  seated in the window  49 , the circlip  34  is positioned so that portions thereof engage with the groove means, here grooves  57 A and  57 B, while other portions thereof contact the portions of the mid-region  36  of the exterior face  56 , thereby to retain the block  33  seated in the window  49 , as illustrated in  FIG. 14 , for example. The circlip  34  is preferably circular in plan view and is preferably circular in cross-section.  
         [0056]     Various circlip configurations and various combinations of circlips and grooves can be employed, if desired. For example, an alternative heart valve prosthesis  90  incorporates an arrangement for groove means, circlip, and block as fragmentarily illustrated in  FIGS. 15 and 16 . In prosthesis  90 , components corresponding to those in prosthesis  21  are similarly numbered but have prime marks added thereto for convenient identification purposes. Here, two circlips  81  and  82  are utilized, each one being retained by a different pair of grooves  83 ,  84  and  85 ,  86  respectively, to position and hold a block  33 ′. The block  33 ′ has a pair of flat faces  37 ′ that meet medially, and each face  37 ′ is in contacting relationship with a different circlip  81 ,  82  in the assembled prosthesis  21 .  
         [0057]     The leaflets  31  and  32  of prosthesis embodiment  21  are each configured so as to be complementary relative to each other so that the leaflets  31  and  32  can be cooperatively disposed across the passageway  43 . The leaflets  31  and  32  can be considered to generally be mirror images of each other, and each has a generally flattened main body portion, and a perimeter that includes an outer rounded edge portion  61 , an inner straight edge portion  63 , and a pair of transversely spaced, generally parallel, straight, medial edge portions  65 ,  66  that interconnect between the opposite end regions of the outer rounded portion  61  and the inner straight edge portion  63 , respectively. The leaflets  31  and  32  cooperate with one another and with the passageway  43  to provide a valve structure that can either close the passageway  43  or open the passageway  43  for passage of blood therethrough in one direction, as shown, for example, by the arrow  35  in  FIG. 1 .  
         [0058]     Each of the leaflets  31  and  32  has a perimeter configuration that is illustrated, for example, by the plan view of leaflet  32  in  FIG. 10 . Thus, each leaflet  31 ,  32  has a perimeter that includes an edge portion  61  that extends arcuately in a nearly circular configuration to define a leaflet outside edge region, and another edge portion  63  that extends straight to define an inside edge region. In the region of each leaflet  31  and  32  located between the end of each straight portion  63  and the adjacent end of each arcuate portion  61 , a relatively short, straight end edge portion  65 ,  66  is defined on each leaflet  31  and  32 , respectively. In each of the straight end edge portions  65 ,  66  of each leaflet  31  and  32 , an integrally formed, flattened, approximately semicircular, preferably perimetrically rounded, outwardly-projecting, ear-like projection  69  is located. The straight edge portions  63  of each leaflet  31  and  32  is preferably beveled so as to permit these edge portions to abut one another in a complementary manner when the leaflets  31  and  32  are in a closed configuration across the passageway  43  of the prosthesis  21 . The arcuate edge portions  61  are preferably provided with a rounded beveled region to permit each of these edge portions  61  to sealingly abut against adjacent regions of the medial side wall portions  46  when, as pivoting occurs, the edge portions abut thereagainst.  
         [0059]     The flat interior face  48  of the integral bearing block  47  and also the flat interior face  55  of the separate bearing block  33  each has formed therein a pair of circumferentially (relative to the ring  30 ) spaced but adjacent cavities  71 ,  72 , respectively. One cavity  71  in block  33  taken with a corresponding opposing cavity  71  in block  47  defines a pivot axis  75  (see  FIG. 2 ) for a leaflet  31  while one cavity  72  in block  33  taken with an opposing cavity  72  in block  47  defines a pivot axis  76  for leaflet  32 . Each ear  69  is configured to extend into a cavity  71  or  72  and to pivot relative thereto. During assembly of the prosthesis  21 , with the circlip  34  removed from the grooves  57 A and  75 B (see  FIG. 14 ), and with the block  33  loosened relative to the window  49 , the ear-like projections  69  of the leaflet  31  are positioned each in a different cavity  71  of each block  47  and  33 , and the ear-like projections  69  of the leaflet  32  are positioned each in a different cavity  72  of each block  47  and  33 . Thereafter, the block  33  is seated in the window  49  and the circlip  34  is associated with the grooves  57 A and  57 B to complete prosthesis  21  assembly. Thus, assembly of prosthesis  21  is completed without flexing or distortion of any pyrolytic carbon component.  
         [0060]     The interrelationship between the leaflets  31  and  32  and the cavities  71  and  72  in the prosthesis  21  is such that the leaflets  31  and  32  are each locatable (by pivoting) across a different portion of the passageway  43  with each ear-like projection  69  being pivotably associated with different one cavity  71  or  72 , as the case may be, in each of the separate bearing block  33  and the integral bearing block region  47  and with the leaflets  31  and  32  being responsive to fluid pressure applied on an upstream side thereof (as indicated by the arrow  35 ) whereby the leaflets  31  and  32  functioning in combination are adapted to extend across and close the passageway  43  and thereby define a valve closed configuration. Leaflets  31  and  32  also pivot and open the passageway  43  and thereby define valve open configurations as illustrated, for example, in  FIG. 12 . The position of a leaflet  31  or  32  is a function of the fluid pressure applied thereagainst. The interrelationship between the leaflets  31  and  32 , the ear-like projections  69 , the blocks  33  and  47 , and the cavities  71  and  72  in the assembled prosthesis  21  is such that the leaflets  31  and  32  cannot slip or change from their pivotable positions during operation of the prosthesis  21 .  
         [0061]     Each leaflet  31  and  32  may oscillate freely between fully closed and fully open positions (see, for example,  FIG. 12 ), and each leaflet  31  and  32  pivots independently of the other about its respective eccentric hinging (or pivoting) axes  75 ,  76  from open to closed positions (inclusive). When viewed from a position along the pivot axis, each cavity  71  and  72  is preferably characterized by a butterfly-type of cavity perimeter configuration and each preferably has an internal spherical configuration that permits each associated ear-like projection  69  to have only limited pivotal movement over a predetermined number of degree angles. At each end of each maximum prechosen pivot, each associated ear-like projection  69  comes into abutment with an adjacent preferably vertically extending side wall portion  77  of the associated cavity  71  or  72 , thereby to achieve a stop that achieves a restricted pivotal movement for each leaflet  31  and  32  across and within the passageway  43  of the ring member  30  in response to fluid pressure differentials developed in the cardiac system of a patient wherein the prosthesis  21  is implanted surgically with the direction of flow of blood being shown by the illustrative arrow  35 . The indicated preferred configuration of the cavities  71  and  72  also serves to avoid potential stagnation of blood which might tend to otherwise occur in unused portions of the cavities  71  and  72  were they to be otherwise configured due to the preferred indicated restricted pivotal movement of the leaflets  31  and  32 . The side portions  77  can be considered to co-act with the ear-like projections  69  to provide stop means for limiting pivotal movements of the leaflets  31  and  32 .  
         [0062]     In each leaflet  31  and  32 , the ears  69  are disposed nearly diametrically opposite to each other (relative to the passageway  43 ). The respective dimensions between components are chosen so that a minute uniform clearance exists between spherical edge surfaces of each ear  69  and adjacent portions of associated cavities  71  and  72 . Curved surface portions of each cavity  71  and  72  and of the associated projections  69  correspond preferably to complementary spherical segments. The cavities  71  and  72  cooperate with each other and with the associated ear like projections  69  to achieve self-aligning bearing assemblies for free and smooth pivotal movement of each leaflet  31  and  32  when in assembled association with the ring member  30 .  
         [0063]     A simple, effective structure is achieved by having one of the two bearing blocks, here block  47 , be an integral part of the ring member  30  while the other bearing block, here block  33  is separate but readily and easily associated the window  49  defined in the side wall  46  of the annular or ring member  30 . The preferred rectangular mating perimeter configurations of the block  33  and the window  49  enhances a firm and stable seating and sealing engagement between the bearing block  33  and the window  49 .  
         [0064]     The two pivot (hinging) axes  75  and  76  are each parallel to the diameter  40  of the ring  30 , and each is spaced at a distance y (see  FIG. 2 ) away from the diameter  40 . The planes defined by the flat interior faces  55  and  48  are each perpendicular to the hinging axes  75 ,  76  and parallel to the edge portions  65 ,  66 . The straight edge portions  65 ,  66  are preferably perpendicular to the respective hinging axes  75 ,  76 , thereby to achieve free rotary movement of each leaflet  31  and  32 . The ear-like projections  69  preferably have about the same thickness as that of the associated leaflet  31  or  32 . Preferably, the outer peripheral arcuate edge portions  61  of the leaflets  31  and  32  each have a curved or rounded profile which is adapted to abut against the adjacent curvature of the inner surface of medial wall  46  at locations thereof where portions  61  rest when in the valve closed position, thereby to avoid jamming between the edges  61  and the wall  32 , particularly due to possible fluidic back pressure that may occur against a leaflet  31  or  32 .  
         [0065]     Each leaflet  31  and  32  has a configuration that covers about half of a selected area across the passageway  43  through the ring member  30 . The straight perimeter edge portions  63  and  64  of the leaflet  31  and  32  are preferably beveled and these edge portions  63  and  64  preferably (as shown) meet together when the leaflets  31  and  32  are in the valve closed configuration, and in this closed configuration each leaflet  31  and  32  is somewhat inclined relative to the other whereby fluid pressure against the faces of the leaflets  31  and  32  urges them into the closed configuration. In this valve closed configuration, the arcuate edge portions  61  and  62  preferably abut and engage (as shown) against the inside of the adjacent portions of the medial side wall portions  46  of the ring member  30  while the respective straight edge portions  65  and  66  are located adjacent to portions of each of respective the flat faces  48  and  54 . In the closed configuration, the leaflets  31  and  32  are preferably configured to provide about their periphery a seal across the passageway  43  that prevents the flow of blood therethrough. Preferably a leakproof joint is achieved that prevents back flow of blood when the leaflets  31  and  32  are in their closed positions.  
         [0066]     The flat chord-like (when the ring  30  is viewed axially) edges  65 ,  66  of the leaflets  31  and  32  as well as to the respective hinging or pivoting axes  75 ,  76  function to wipe and to clean blood on the flat faces  48  and  55  of the bearing housings  47  and  33  during each oscillation of the leaflets  31  and  32 . The preferably spherically curved peripheral edge of each ear-like projection  69  functions to sweep the adjacent spherical surfaces of each cavity or recess  71  and  72 .  
         [0067]     Various methods of the prior art can be used in fabricating pyrolytic carbon containing components employed in the present invention. Typically, a component with a carbon surface is heated to beyond 1,000° C. to achieve a hard and naturally polished surface. Higher temperatures give greater hardness depth relative to the surface. See, for example, Bokros U.S. Pat. No. 3,676,179.  
         [0068]     For example, in one process, carbon black powder is pressed under high pressure to make rods or other shapes. The shapes are machined and articles (components) are produced. In the present situation, the leaflets and the ring member are produced. These articles are then heated in a controlled atmosphere to 1,200° C. or above, the temperature selected being influenced by the desired structure. Thus, the resulting pyrolytic carbon components of an inventive prosthesis embodiment, such as the leaflets, for example, are characteristically heat treated and hardened but not coated using conventional technology. Typically, the pyrolytic carbon components are inert and light in weight and density.  
         [0069]     To achieve a precisely dimensioned product, one may position a preformed but unfinished (or “blank”) separate bearing block in the bearing block window of a preformed but unfinished (or “blank”) annular ring structure and retain the unfinished bearing block in position with the circlip. Surface portions of this combination of ring structure and separate bearing block can then be machined and the bearing recesses or cavities formed therein. Thereafter, the circlip can be removed, the separate bearing block loosened from the window, the leaflet ear-like projections duly positioned in the recesses, and the separate bearing block reseated in the window and retained by the circlip to complete prosthesis assembly. The steps of this method of prosthesis preparation can be, for example, characterized as follows:  
         [0070]     (a) forming in a blank for the annular structure the bearing block receiving window including window perimeter portions;  
         [0071]     (b) forming perimeter portions about a blank for the separate bearing block, these perimeter portions being cooperatively engageable with the window perimeter portions whereby the blank for the separate bearing block is seatable within the bearing block receiving window;  
         [0072]     (c) forming groove means in the blank for the annular structure, the groove means being adjacent to the bearing block receiving window, and associating circlip means with the groove means, whereby said blanks are associated together in a combination;  
         [0073]     (d) machining surface regions of said combination whereby 
        a flat interior face is defined upon said blank for said separate bearing block,     said integral bearing block is defined in said blank for said annular structure with a flat interior face for said integral bearing block that is in spaced, parallel relationship to said flat interior face of said separate bearing block,     each of said flat interior faces is parallel to a longitudinal axis defined in said annular structure; and     each of said flat interior faces has defined therein said pair of spaced bearing recesses, thereby to form said annular structure and said separate bearing block;        
 
         [0078]     (e) said circlip means is dissociated from said groove means and said separate bearing block is separated from said annular structure while said ear-like projections of each of said leaflets are pivotably each engaged with one said bearing recess in each said bearing blocks; and  
         [0079]     (f) said separate bearing block is reengaged with said window and said circlip means is reassociated with said groove means, thereby to fabricate said prosthetic heart valve.  
         [0080]     Various other and further embodiment applications, structures and the like will be apparent to those skilled in the art from the teachings herein provided and no undue limitations are to be drawn therefrom.