To test the hypothesis that carnitine is decreased in the myocardial tissue of patients with end-stage congestive heart failure (CHF), left ventricular myocardial carnitine was measured in 51 patients undergoing orthotopic cardiac transplantation. The study group included patients with idiopathic dilated cardiomyopathy, coronary artery disease, myocarditis and rheumatic heart disease. Myocardial carnitine varied in different cardiac chambers. In normal control hearts, the left and right ventricular total carnitine was similar, but the ventricles had higher levels than the atria (p less than 0.005); in 30 hearts in CHF, the left ventricular total carnitine was higher than in the right ventricle (p less than 0.001) and both ventricles had higher total carnitine than the atria (p less than 0.005). Only 7 of 51 patients with CHF had low myocardial carnitine, whereas plasma carnitine was elevated in all diagnostic groups of end-stage CHF studied.