Heart attack.
One of the major causes of death in the U.S., a heart attack occurs when blood flow to a section of heart muscle becomes blocked, preventing it from receiving the oxygen it needs. If not treated relatively quickly, the muscle will become damaged and possibly die.
In doubt? Call 911.
A heart attack (also known as myocardial infarction) is a serious and often fatal condition. If you think you or someone with you is experiencing a heart attack, you should seek medical attention immediately by dialing 911. If the blood flow can be restored in time, damage to the heart can be limited or prevented.