National Heart Lung & Blood Institute - Polycythemia Vera (PV)

Polycythemia (POL-e-si-THE-me-ah) vera (VAY-rah or VE-rah), or PV, is a rare blood disease in which your body makes too many red blood cells.

The extra red blood cells make your blood thicker than normal. As a result, blood clots can form more easily and block blood flow through your arteries and veins. This can lead to heart attack and stroke.

Thicker blood also flows more slowly to all parts of your body, preventing your organs from getting enough oxygen. This can cause other serious complications, such as angina (an-JI-nuh or AN-juh-nuh) and heart failure.