LDL (low density lipoprotein), a substance that is used to transport cholesterol from the liver to tissues throughout the body, is also known as "bad cholesterol." This "LDL cholesterol" can build up on the walls of your arteries and is the main source of plaque buildup. The more LDL you have in your blood, the greater your risk of heart disease. Lifestyle changes and cholesterol medication are proven ways to decrease it.