Background There are almost no reports on the physiological effects of the various electric massage devices available on the market. This report describes the effects on peripheral vascular circulation and autonomic-nervous system activity of a pulse-synchronized air-massage (PS-AM) device in which cuffs apply air pressure cyclically to the lower limbs only during the cardiac diastolic phase. Methods and Results The PS-AM device consists of a main unit with a pulse-wave detector that uses the pulse-wave to activate an air pump only during the cardiac diastolic phase. Pressure is applied sequentially from the feet to the thighs by 4 pairs of cuffs attached to the main unit. The study was carried out on 55 volunteers (19 males, 36 females). A laser Doppler flow-meter attached to the subjects' toes was used to measure blood flow (BF), while ECG, blood pressure and cardiac autonomic nerve activity [parasympathetic nerve activity (high-frequency component (HF))] were measured by a multibiomedical recorder (TM2425). The measurements were made for a total of 45 min consisting of three 15-min periods: before massage, during PS-AM, and after massage. BF increased 139±33 (SD) % in males and 154±44% in females during PS-AM, with a significant correlation being observed between BF and HF during PS-AM (p