INTRODUCTION: The depolarisation signal is initiated on the surface of the muscle fibers, then it stimulates the release of Ca2+ from the endoplasmic reticulum cisterns and thus spreads through the muscle fiber. After the depolarization, the membrane of the sarcoplasmic meshes stimulated with the nerve stimulation, the Ca2+ ions that have accumulated in tanks of sarcoplasmic mesh, discharge passive into the nearby areas of the overlapping thick and thin filaments, and there they are bound to troponin and allow actin to connect with myosin. When the depolarization of the membrane is complete, the sarcoplasmic mesh drains calcium that actively returns to the tank and than the contraction is ceased. It is known that hypercalcemia in the cardiac muscle leads to shortening of the refractory period and to the slow implementation of the cardiac impulse which results in the occurrence of arrhythmias. With arrhythmia, hypercalcemia also stimulates the contractions of the heart and can cause hypertension. CD34 cells are used as markers for the identification and isolation of certain hematopoietic stem and progenitor cells. Caveolae of renal endothelial and epithelial plasma membranes are particularly abundant with neutral glycosphingolipid CD77. AIM OF RESEARCH: To determine the expression of CD34 and CD77 markers on the plasma membrane of cardiac cells in hypercalcemic rats compared with the expression on the plasma membrane of cardiac cells in control rats. MATERIALS AND METHODS: Male Sprague – Dawley rats, 6 weeks old separated in 2 groups: the examination group undergone the hypercalcemic treatment (n=8) and untreated controlled group (n=9). To achieve hypercalcaemia, to the hypercalcemic group was given water that was rich with CaCl2. The period in which the rats were drinking water enriched with CaCl2 was 14 days. After sacrifice, the heart tissue was removed from the rats in the control group and in the hypercalcemic group. All animals were sacrificed in prolonged anesthesia (diethylether). The subsequently prepared isolated heart cells were incubated with two antibodies for the double staining of cells: CD34 antibody conjugated with PC5 and CD77 conjugated with FITC, then analyzed by flow cytometry. RESULTS: Percentage of ionized calcium in the hypercalcemic group was 48 ± 0.30% and in the control group 44 ± 0.96% (P = 0.013). In the heart of hypercalcemic rats the share of CD34 + CD77- cells were slightly reduced compared to the control group. CONCLUSION: Reduction in the percentage of CD34+CD77- cells in the heart of hypercalcemic rats with regard to the control group was not statistically significant, but these data confirm the latest researches which have shown that the splitting of vascular endothelial cadherin was caused by the influx of Ca2+.