The influence of profuse sweating on systolic time intervals was investigated. Systolic time intervals were recorded in 21 healthy men before and after sauna bathing. After sauna bathing the ejection time was significantly shortened and the pre-ejection time and ratio of pre-ejection time to ejection time (PEP:ET) were significantly increased. The upper limit of the PEP:ET ratio is generally believed to be 0.42 and this ratio increases when left ventricular performance is impaired. Before sauna bathing the PEP:ET ratio was less than 0.42 in all 21 men, but after sauna bathing it was greater than 0.43 in six (28.5%) of them. Systolic time intervals measured after profuse sweating can give a false impression of cardiac function.