Day-by-day changes in ventricular-ejection time/heart-rate ratio (VET/HR) and in ejection time index (ETI), determined by an impedance method in a decompression chamber, were more labile in the mountaineers who had experienced high altitude (above 6,000 m) within the past 1 year, and the ETI values in the first hypoxic exposure were significantly high in these subjects, though close to those of the non-experienced group in the later exposures, suggesting that the effect of hypoxic acclimation on cardiac function might remain at least 1 year after return to sea level.