― ViaHow do you know when that the funny feeling in your chest is not heart burn or indigestion but truly a heart attack? What exactly is a heart attack? A heart attack (or myocardial infarction) occurs when blood flow to a portion of the heart is blocked, usually by a blood clot. Coronary arteries are what supply oxygen-rich blood to our heart. Blocking these arteries is what causes heart attacks, heart failure, angina (chest pain) and even sudden death. When these arteries are blocked in the [...].