Echocardiograms were performed on 111 prosthetic porcine valves in mitral position and 25 in aortic position. Satisfactory tracings were obtained in 68% of the mitral and in 80% of the aortic prosthesis. The characteristic appearance of the porcine prosthesis consists of two lines parallel to each other which represent the stent; the valve cusps reflect much thinner echoes with a box-like pattern similar to that of the normal aortic valve. The distance between the cusps varied from 12 to 17 for the mitral prosthesis and from 11 to 15 for the aortic prosthesis. The range of these values as well as the range of other parameters which were measured varies widely. We suggest therefore that a post-operative echocardiogram should be performed to get a baseline pattern useful for comparison with following controls.