Expecting activation of myocardial energy liberation, coenzyme Q was applied as a treatment to 55 patients suffering from congestive heart failure. Daily doses of 50 to 100 mg of coenzyme Q7 were injected intravenously in 21 cases for 3 to 35 days. Daily doses of 60 mg of coenzyme Q7 were administered perorally in 17 cases for 14 to 196 days. Daily doses of 30 mg of coenzyme Q10 were administered perorally in 17 cases for 7 to 182 days. Clinical effects were evaluated within 4 weeks by the criteria using a scoring method of severity of congestive heart failure which was devised by the authors. In summary a certain effect was found in 20 cases and a mild effect was observed in 29 cases. No significant changes were observed in heart rate and blood pressure. Exanthema appeared in 2 patients of the group of coenzyme Q7 intravenous injection. In conclusion the therapeutic effect of coenzyme Q was thought to be mild but stable in supplement to digitalis therapy in cases of congestive heart failure.