Anginal pain that occurs only with exertion is usually caused by a fixed blockage in one or more of the coronary arteries. Pain that occurs without exertion (., at rest) may result not only from plaque build-up, but also from a blood clot that has formed in the artery. If the blood clot grows to completely block the artery, it can cause a heart attack. Anyone experiencing angina at rest should seek prompt medical attention. Medications are available to help prevent blood clots from completely blocking the coronary artery and causing a heart attack.