Polycythemia increases blood viscosity, slowing down the blood flow that carries oxygen to the heart, brain, and other vital organs; this can lead to insufficient oxygen reaching the organs. Furthermore, increased blood viscosity significantly raises the risk of clotting, which can lead to severe complications such as stroke and heart attack. If left untreated, polycythemia is a dangerous condition and carries a long-term risk of transforming into more serious blood disorders such as myelofibrosis or acute leukemia.