Abstract: Coenzyme Q10 is recommended in various disorders. One of this in congestive heart failure, the purpose of this study is to provide the efficacy of this drug in patients with hearth failure or not. To determine the effect of coenzyme Q10 on sign and symptom and ejection fraction. This 12 months randomized double blind placebo clinical trial was done in University of Mazandaran, we choose 100 patients who had congesting heart failure with New York Heart Association class II and III symptoms and ejection fraction = 40%, aged more than 40 years old, these patients divided into 2 groups, 50 patients received coenzyme Q10 (capsule 100 mg) the other 50 patients received placebo. Left ventricular ejection fraction (measured by Echocardiography) and physical exam done each 3 months. Coenzyme Q10 administered orally has favorable actions on the sign and symptoms of patients with H. F in the beginning of study, SD (�) EF in the control group was 30�10.7 and in the case was 33.2�8.6 and after treatment EF increased in case groups (p<0.05). Coenzyme Q10 therapy in patients with CHF can be recommended as adjuvant therapy. Now we cannot use it as monotherapy until additional clinical trial demonstrate beneficial effects of it.