The aim of the work: Electrical activity assessment of the heart in the 24 hour rhythm aspect during pregnancy in healthy women, determining the critical phase of development, that is to say cardiac insufficiency. Materials and mehods: The surveys were made on 45 healthy women of 38-40 week gestation period. The electrocardiogramm in 12 derivations was registered at “Mingograf-34” (Siemens-Elema) along 24 hours, at 7, 11, 15, 23 and 2. Results: The electrocardiographic investigations have ascertained the fact that in healthy women at 7 o’clock in the morning was present a uniform sinus rhythm with normal cardiac contraction frequency; duration of intraatrial, atrioventricular and intraventricular conductibility, also electrical systole within the norm limits; maximal amplitude of P wave in derivations II, aVF, V2-3, and of R wave in derivations II, aVF, V4-5, and wave T- in derivations I, II, V5. Conclusions: 1. In the period of physiological pregnancy in healthy women the electrical activity of the heart possesses a strictly determined chronobiological rhythm with the maximum cardiac function at 3 o’clock in the afternoon and 11 o’clock at night and the minimum at 11a.m, 7p.m, and 2a.m. 2. In healthy pregnant women with 38-40 week physiological gestation period during the day at about 11 a.m, 7 p.m, and 2 a.m, are critical hours where there is a possibility in cardiac insufficiency development on the background of decreasing heart’s electrical activity.