A cardiologist is a medical doctor who specializes in diagnosing and treating diseases of the heart and blood vessels. As such, a cardiologist's concern would include the AORTA, which is the main artery that carries oxygen-rich blood from the heart to the rest of the body; the HEARTBEAT, which is the rhythmic sound made by the heart as it pumps blood; and CLOTS, which are masses of blood cells that can form in the arteries and veins and can cause blockages.