Heart disease, also known as coronary artery disease (CAD), is primarily caused by plaque building up on the inner walls of the arteries and reducing the amount of blood that can get to the heart. It is the cause of most heart attacks. Plaque is made up of fat, cholesterol, calcium, and other substances found in the blood. When plaque accumulates, it narrows and hardens the arteries, and limits blood flow. This decreases the oxygen supply to the heart muscle. When the heart muscle does not get enough oxygen, two conditions can develop: angina and a heart attack. Angina is a condition in which the heart muscle does not get sufficient oxygen. This causes chest pain or discomfort. A heart attack can occur if an artery closes all the way or a clot blocks the blood flow. When this happens, the heart muscle does not get oxygen and cells begin to die. Certain factors, such as age and family history, increase the likelihood of developing CAD. Men older than 45 and women older than 55 are at higher risk for CAD. If heart disease was diagnosed in your father or brother before age 55, or if heart disease was diagnosed in your mother or sister before age 65, you'll need to take special precautions for avoiding it. The key risk factors for CAD that can be influenced by lifestyle choices include the following: High cholesterol: Two of the main forms of cholesterol are "bad" cholesterol, or low-density lipoproteins (LDL), and "good" cholesterol, or high-density lipoproteins (HDL). LDL carries the form of cholesterol that builds up in the arteries. HDL carries cholesterol that is being removed from the body, which keeps it from building up on the walls of arteries. A low HDL level (less than 40 mg/dL in men; less than 50 mg/dL in women) increases the risk for heart disease. If you have too much LDL cholesterol (100mg/dL or higher), it can accumulate with other substances in the lining of the arteries. This makes the arteries narrower and eventually blocks the flow of blood. High blood pressure: Your heart works harder when your blood pressure is at 140/90 mm Hg or greater. This level is called high blood pressure. When your blood pressure is high for an extended time, the heart can enlarge and arteries can become scarred and hardened. Obesity: Your risk of heart disease increases if you're overweight or obese. Obesity raises cholesterol and blood pressure, and it can lead to diabetes, another risk factor for heart disease. Diabetes: Diabetes makes it easier for plaque to form in your arteries. Because of this, it increases the risk for heart attack. People with diabetes are two to four times as likely to have a heart attack as is someone who does not have diabetes. The American Heart Association recommends regular screening for risk factors beginning at age 20. Screening includes measuring blood pressure, body mass index, waist circumference, and pulse every two years, and getting a cholesterol profile and glucose test (a simple blood sugar test) every five years. Your doctor may want you to have more frequent screenings or visits if you have a family history of heart disease, diabetes, high blood pressure, high cholesterol, or other health problems.