A calf with a biolized TAH was maintained in reasonably good physiological condition for a major portion of a 145-day experiment as indicated by near normal growth rate and laboratory data. The mechanism for the high CVP and CBV at the beginning and end of the experiment were correlated with protein metabolism. No evidence of thromboembolism was found at autopsy and only modest congestion with minimal parenchymal damage was observed. The cardiac prosthesis itself was free of thrombus, although slight calcification was found on the valves and diaphragms. The pump performance, however, remained satisfactory. In addition, endothelialization appeared to be starting on a portion on the inside of the pump.