The diving reflex (DR) is a set of protective functional alterations aimed at economizing oxygen consumption while diving. This effect is achieved through reflexive deceleration of the heart’s rhythm, constriction of peripheral vessels (PVs) and selective redistribution of blood to those organs which are most vulnerable to hypoxia (the brain and heart). The effectiveness of DR as a protective mechanism depends on the nature of vegetative and humoral regulation in the cardiovascular system. The aim of this study is to determine whether protective cardiovascular mechanisms when diving vary in people with different polymorphisms of the BDKRB2 and ACE genes. 96 volunteers (students; aged 18-24) were examined. These subjects were not adapted to diving. DR was activated by submerging their faces in cold water (12-14oC) under laboratory conditions. ECG records were taken for the resting state, during diving simulation (DS) and after apnea. The minute volume of blood flow (MVBF) was also determined for these states using rheography, and the blood supply to peripheral vessels was measured indirectly using the pulse wave amplitude (PWA) of the photoplethysmogram (PPG). Vascular tone was calculated from the time of its spread (the pulse transit time, PTT). Blood pressure was recorded. DNA samples from all patients’ blood were isolated using phenol-chloroform extraction. I/D polymorphism (rs4340) of the ACE gene was analysed using PCR. The results were analysed using Mann-Whitney nonparametric tests (paired comparisons). According to the results of the ACE polymorphism study, significant differences in PTT were found between I/D (n=27) and I/I (n=23) alleles at the control level (CL) and during DS (p<0.05). They were also found between I/I and D/D (n=21) at CL, during DS and during recovery (p<0.01). When BDKRB2 alleles were studied, significant differences in PWA between T/C (n=35) and C/C (n=24) were found in all dives and during recovery (p<0.05; p<0.01). They were also found between T/T (n=13) and C/C after two dives and two periods of recovery (p<0.01). A significant decrease in MVBF and PWA (p<0.05; p<0.01) occurred in the groups with I/D, I/I and T/C polymorphisms during DS, which is similar to that found in diving animals. In subjects with I/D and T/C polymorphisms, PWA increased in the recovery process when compared with CL (p<0.01). This reflects an increase in blood volume in the PVs and indicates oxygen debt formed during DS. When diving is simulated, constriction of PVs was observed in all subjects examined, but its severity had significant individual differences. Studies have shown that the most effective defence mechanisms against hypoxia are those which develop when diving in people with a heterozygous combination of alleles.