From April 1978 through December 1980, 216 Carpentier porcine xenografts (144 mitral, and 72 aortic) were inserted in 189 patients (117 mitral, 45 aortic, and 27 mitral and aortic). The hospital mortality was 8.5% (10/117) for mitral patients, 6.6% (3/45) for aortic, and 3.8% (1/27) for mitral and aortic. Of 175 patients discharged from the hospital, there were 16 late deaths, which represents an incidence of 1.9% per patient-year (10/107) for mitral, 0.9% per patient-year (2/42) for aortic, and 3.4% per patient-year (4/26) for mitral and aortic, patients. There were 13 thromboembolic events in 10 patients. This represents a linearized incidence of 2.3%, and 0.5% per patient-year for mitral and aortic patients, respectively. One of the accidents was fatal, and 3 of the 10 patients were on a regimen of anticoagulation at the time of embolism. Seven instances of valve endocarditis oc-curred in 4 mitral, 1 aortic, and 2 mitral and aortic patients (5 mitral, 2 aortic, and 2 mitral and aortic). This represents a linearized incidence of primary tissue failure of 0.96%, 0.96% and 1.7% per patient-year for mitral, aortic, and mitral and aortic patients, respectively.