We compared the effect of oral administration of taurine (3g/day) and coenzyme Q₁₀ (CoQ_<>) (30 mg/day) in 17 patients with congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy, whose ejection fraction assessed by echocardiography was less than 50%. The changes in echo-cardiographic parameters produced by 6 weeks of treatment were evaluated in a double-blind fashion. In the taurine-treated group significant treatment effect was observed on systolic left ventricular function after 6 weeks. Such an effect was not observed in the CoQ₁0-treated group.