The influence of exogenous free fatty acid (FFA) on hypoxic myocardial function was studied in isolated, isometric rat papillary muscles. In 95 % O<sub>2</sub>, no difference in developed tension was noted between muscles in glucose (5 mM) or FFA (oleic acid 1,800 µM ) buffer. During hypoxia (20 % O<sub>2</sub>), muscles in FFA or no substrate buffer developed less tension and in subsequent reoxygenation, recovered less function than muscles in glucose buffer (with or without added FFA). Prior stabilization in glucose eliminated these differences for muscles supplied with FFA or no substrate during hypoxia, although recovered function for muscles with no substrate remained deficient. Muscle thickness correlated inversely with control developed tension (g/mm<sup>2</sup>), but did not correlate with percent depression during hypoxia. This study failed to demonstrate a depressant effect of exogenous FFA on the mechanical performance of rat myocardium during hypoxia.