Myocardial triglyceride levels in rats fed a high erucic acid rapeseed oil diet for three days were five times higher than in controls. The incorporation of erucic acid and, to a lower extent, some unsaturated fatty acids was increased, as well as total cholesterol content, compared to controls. The presence of 5% carnitine in the diet partially prevented these effects. It is assumed that carnitine may be a rate limiting factor in the myocardial catabolism of unsaturated fatty acids and particularly erucic acid, when these substance are ingested in supraoptimal amount.