The purpose of this study is to evaluate the ability of propionyl-L-carnitine, a carnitine derivative to prevent cardiac dysfunction induced by erucic acid and streptozotocin treatment in rats. Rats were fed for 10 days with normal or 10% erucic-acid-enriched diet with or without propionyl-L-carnitine injected intraperitoneally (1 mM/kg daily). Another group of rats was injected for 8-10 weeks with streptozotocin (65 mg/kg) with or without propionyl-L-carnitine intraperitoneally injected at the same dosage. Thereafter the animals were sacrificed and the hearts isolated and perfused aerobically. When isovolumic measurements of left ventricular function were applied, there was no difference in mechanical activity between treated and control hearts. On the contrary, when pressure-volume curves were determined in the paced hearts, the pressure developed by hearts from erucic acid-treated or diabetic rats was reduced. Propionyl-L-carnitine always produced positive inotropy. This was true for the control-saline treated rats that received the drug, as well as for the hearts isolated from cardiomyopathic animals. These data suggest that propionyl-L-carnitine, when given chronically, is able to overcome myocardial dysfunction caused either from erucic acid treatment or diabetes.