A group of 11 healthy subjects aged 32–48 years was studied by dynamic electrocardiography. Electrocardiogram (ECG) was recorded on CM5 lead for 14 sec every 15 min during 24 h. All the subjects were under a different sleep‐wakefulness cycle, sleeping at different hours of the day. The time of midsleep was used to reference the chronobiologic evaluation of the parameters studied. Single cosinor analysis of the data revealed statistically significant circadian rhythms in: (a) heart rate (HR) and duration of QT interval for all the subjects studied; (b) ST segment displacement for the 2 subjects who were found to have it; (c) R and T waves voltage for 10 and 7 subjects, respectively. On the contrary, population mean cosinor analysis of the same data revealed statistically significant circadian rhythms only in HR and in the duration of QT interval. We conclude that only HR and QT interval relate to the sleep‐wakefulness schedule.