Today, the prospect of long-term interplanetary missions becomes relevant, that is why it is necessary to understand the changes in the cardiovascular system (CVS) that would occur in hypomagnetic environment. The study was aimed to assess the changes in the CVS mechanisms underlying formation of heart rate variability and bioelectric processes in the myocardium under conditions the 350-, 650-, and 1000-fold reduced Earth’s magnetic field. The experiment (2023) involved 6 male volunteers aged 26–37 years, in whom electrocardiography was continuously performed throughout 32 h. The data obtained were assessed by cluster analysis and analysis of variance. It was found than male volunteers, who belonged to the group showing predominance of parasympathetic effects, had enough functional reserve for critical values (exposure to the up to 1000-fold reduced magnetic field). In volunteers showing predominance of sympathetic modulatory effects, the adaptive response maintenance was ensured by the metabolic regulatory circuit. In this group, the response to the reduced magnetic field exposure was quite pronounced at the threshold of its 350-fold reduction. Our pilot experiment reflecting the effect of the reduced Earth’s magnetic field on the CVS is crucial for development of the concept of further experimental exposures related to magnetic field reduction benefiting space physiology and medicine.