Abstract The Hancock modified-orifice porcine valve was fabricated as a result of documented obstruction of the Hancock standard porcine valve in small sizes related to the retained muscle bar of the right coronary cusp. We implanted the first clinical Hancock modified-orifice valve in 1976, and have used this valve for aortic valve replacement to the present time. This analysis compares and contrasts the clinical performance of 401 Hancock standard and 385 Hancock modified-orifice valves over a period of 10 years. Statistical significance in actuarial curves at 120 months was noted in long-term survival and thromboemboli. There was a slightly smaller amount of structural valve degeneration and incidence of reoperation with the modified-orifice valve compared with the standard valve. The Hancock modified-orifice valve has proven to be a satisfactory aortic valve replacement device, and its complex fabrication has withstood the test of time.