Blood doping - Wikipedia, the free encyclopedia

EPO is also not free of health hazards: excessive use of the hormone can cause polycythemia, a condition where the level of RBCs in the blood is abnormally high. This causes the blood to be more viscous than normal, a condition that strains the heart. Some elite athletes who died of heart failure—usually during sleep, when heart rate is naturally low—were found to have unnaturally high RBC concentrations in their blood^[1].

Highlighted by brainz51