It is well known that by improving mitochondrial bioenergetics, Coenzyme Q10 improves the systolic function in heart failure. The aim of this study was to see whether it benefits the diastolic dysfunction in hypertrophic cardiomyopathy (HCM) cases since diastolic relaxation also requires energy like the systole. 200 mg/day of CoQ10 was added to the conventional treatment in 46 patients with HCM diagnosed clinically and by echocardiography and by excluding cases of long standing hypertension. A comparable group of 41 age/sex matched cases received only conventional therapy. There was a significant improvement in the parameters like NYHA class > or = 1, in quality of life (QOL) on 6 minutes walk test, in diastolic dysfunction by > or = 1 parameter and in MR > or = 1 grade. Post treatment echocardiogram showed significant reduction in left ventricular outflow tract (LVOT) gradient > or = 15 mm Hg in obstructive cases (12 out of 46) in the treatment group. The mean interventricular septal thickness (IVS) showed a 22.4% reduction (p < 0.005). The mean posterior wall thickness showed a 23.1% reduction (p < 0.005). No patient in the treatment Group had ventricular tachycardia (VT) whereas 4 cases in the control group had VT. In both groups 1 patient was lost due to sudden cardiac death (SCD).