<p> Various areas of studies on the natural and the prosthetic aortic valves are reviewed. </p> <p> A microtensile technique devised to investigate the inhomogeneous and anisotropic material properties of a porcine aortic valve's leaflets is described. Also, the theory and apparatus of a new stereophotogrammetric technique to define points in space by their Cartesian coordinates is introduced. The technique is used to investigate the local surface strains and curvatures of a porcine aortic valve's leaflets from 0 to 120 mm. Hg. in-vitro. </p> <p> It is found that the valve leaflets display marked inhomogeneity and anisotropy (orthotropy is assumed) in the elastic moduli and transition strains. For the non-coronary leaflet, the radial post-transition moduli vary from 42 to 215 gm/mm² with a mean of 111 gm/mm² (s.d. = 43 gm/mm²); and the radial transition strains vary from 30% to 70% with a mean of 58% (s.d. = 7%). Areas nearer the leaflet's coaptation edge tend to exhibit lower radial transition strains than the annulus edge. The central region of the leaflet is found to be the stiffest. For the same non-coronary leaflet, the circumferential post-transition moduli vary from 220 to 590 gm/mm² with a mean of 342 gm/mm² (s.d. = 118 gm/mm²); and the circumferential transition strains vary from 22% to 47% with a mean of 33% (s.d. = 3%). </p> <p> Inhomogeneity between leaflets is also observed; preliminary results seem to suggest that the non-coronary leaflet is the stiffest in the radial direction and the least stiff in the circumferential direction. In comparison, the right coronary leaflet exhibits the largest radial transition strains (~80% ) and the smallest circumferential transition strains (~25%). </p> <p> For the diastolic valve in-vitro, the circumferential strains are less than 10% at all pressures; therefore , this suggests pre-transition behaviour during diastole which is contrary to the general belief. Radial strains at diastole vary from 10% to well over 100% and show a definite tendency to increase from the sinus-annulus edge to the coaptation edge. The non-coronary leaflet is the least strained of the leaflets (10% to 60% at diastole). </p> <p> The determination of pre-or post-transition state at diastole is discussed and the implications of the results on stress analyses and trileaflet valve designs are noted. </p> / Thesis / Master of Engineering (ME)