*Department of Physiology, Faculty of Science, Prince of Songkla University, **Department of Physiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
Effects of supplementation of vitamin B to average daily intake in normal Thais were studied. The investigation was made on cardiac functions. The cardiac efficiency was assessed with noninvasive technique by measuring systolic time intervals. Supplementation of 30 mg per of vitamin B1 in thirty healthy subjects for a period of 60 days produced some effects on cardiac performance as seen from distinct changes of systolic time intervals. Left ventricular ejection time significantly lengthened. Per-ejection period and isovolumic contraction time significantly shortened. The changes of these three systolic time intervals reflected improved myocardial performance, indicating the improvement of contractility and increase of output of the heart.