In pregnant women during 8th and 9th month of pregnancy simultaneous registrations of the maternal and the fetal electrocardiograms were carried out, generally by systematic long-term studies during night rest. It could be proofed by examinations of the frequency distribution of the maternal R-peaks within the fetal cardiac cycle as well as of the frequency distribution of the fetal R-peaks within the maternal cardiac cycle that around a whole number frequency relationship of both of the heart rhythms a phase coordination between maternal and fetal heart actions occurs, leading to a preference of a defined phase relationship. According to the detected phase relationship it can be presumed, that the fetal rhythm is triggered by the guiding maternal pulse wave rhythm within a small range.