Clinical experience with the Hancock porcine bioprosthetic heart valve was reviewed in 467 patients (254 men and 213 women, 18--84 years old, average, 56 years) who received 528 valves from January, 1972, to January, 1978. Associated procedures, including coronary bypass graft, ascending aortic aneurysm, and valvuloplasty were done in 102 of the 467 patients (22%). The overall operative mortality was 25/467 (5.6%), 12/226 (5.3%) for aortic valve replacement (AVR), 11/183 (6%) for mitral valve replacement (MVR), and 2/58 (3.4%) for multiple valve replacement. The first 323 patients with a minimum follow-up of 16 months (16--75 months, average 33 months) were analyzed for survival and thromboemboli. Actuarial survival at 66--75 months was 75.7% for AVR, 79% for MVR, and 75.8% for multiple valve replacement. Emboli per 100 patient-years was 0.55 for AVR (no anticoagulants), 3.9 for MVR, and 4.8 for multiple valve replacement (anticoagulants for atrial fibrillation patients only); emboli occurred only in patients with atrial fibrillation. There were seven of 528 primary dysfunctional valves (1.3%): calcification in two, tissue failure in two, and fibrosis in three. A hemodynamic study of four patients with a 21 mm Hancock Modified Orifice aortic valve prosthesis showed improved orifice areas (greater than 1.3 cm2) over the standard aortic valve. The Hancock porcine xenograft bioprosthetic heart valve has been a durable heart valve in excess of 6 years and has a low associated incidence of thromboemboli in patients off anticoagulants except in those with chronic atrial fibrillation.