This brings about the early symptoms of PV, including dizzinessand shortness of breath. Thicker blood is also more likely to form a clot -- a clump of blood that stops up a vein or artery.

However, when a blood clot in the heart travels and lodges in, or embolizes to, the coronary artery, it causes a heart attack. Symptoms of a heart attack include the following: Chest pressure or ...

With two high-profile NBA stars suffering from blood clots recently, we asked doctors how they happen and if they are occurring more often.