Category A - full version without watermark 720x576 (check terms and conditions at The version with watermark is for free to embed. There are two types of cholesterol: good and bad. Its important to understand the difference, and to know the levels of good and bad cholesterol in your blood. When too much LDL (bad) cholesterol circulates in the blood, it can slowly build up in the inner walls of the arteries that feed the heart and brain. Together with other substances, it can form plaque, a thick, hard deposit that can narrow the arteries and make them less flexible. This condition is known as atherosclerosis. If a clot forms and blocks a narrowed artery, heart attack or stroke can result. About one-fourth to one-third of blood cholesterol is carried by high-density lipoprotein (HDL). HDL cholesterol is known as good cholesterol, because high levels of HDL seem to protect against heart attack.