Mechanical cardiac valvular prostheses continue to be more popular than bioprostheses for heart valve replacement operations. Five different brands of mechanical heart valves are now approved for implantation in the United States: Starr-Edwards models 1260 and 6120, Medtronic-Hall, St. Jude Medical, Omniscience, and CarboMedics. Each model of mechanical valve has certain positive and negative attributes, but none is functionally mechanically perfect. A review of the published long term results with these valves favors the Medtronic-Hall and St. Jude Medical valves. A new method of assessing the thrombogenic potential and requirement for anticoagulation of the different mechanical valves, namely the composite thromboembolism and bleeding index, is proposed. Evaluation of the new index demonstrates a modest advantage for the Medtronic-Hall valve, particularly in the aortic position.