Cholesterol is a fat-like substance that is in our blood. Our bodies naturally produce some cholesterol. The other portion comes from animal products such as meat, eggs, butter, cheese, and whole milk. Foods from plants do no contain cholesterol. When you have a high level of cholesterol in your blood, it builds up in the walls of your arteries. Over time, this buildup causes the arteries to narrow and become hard, which slows down blood flow to the heart. This reduced blood flow can cause chest pain when you exercise, walk, or exert yourself in any way. If the blood flow is completely blocked off to a portion of your heart, a heart attack can occur.