Research has proven that cholesterol levels are connected with heart disease. One project in Massachusetts has studied the same group of man and woman since 1948. The researchers have found that the people who have high levels of cholesterol have more heart attacks. A natural substance in the blood, cholesterol comes from the liver. The amount of cholesterol is affected by diet and by physical qualities we inherit from our parents. One kind of cholesterol sticks fat to the walls of arteries, making them smaller and finally blocking them. It produces a condition Aut called "hardening of the arteries," which causes heart attacks. With tiny cameras, doctors can see blood circulating through the heart valves. Angiograms are x-rays of the heart arteries. They show fat deposits and blockages caused by high cholesterol.