The design of an intrathoracic left ventricular assist device (LVAD) is briefly described. The unique feature of the LVAD is that all blood-contacting surfaces are biolized, having either chemically treated natural tissues or protein coatings. The blood-contacting surface of the housing is glutaraldehyde-treated pericardium and is covered with natural rubber and polyurethane. Tri-leaflet valves fabricated from human dura mater are used at the pump inlet; glutaraldehyde-treated bovine aortic valves are used at the outlet. The pumping diaphragm, made of polyolefin rubber with a textured surface, is coated with gelatin and treated with glutaraldehyde. Anticoagulants are not used with this device. Extensive in vivo and in vitro testing in the development of the pumps led to the current configuration having good performance, long life, and improved blood compatibility.