http://www.nhlbi.nih.gov/health/dci/Diseases/HeartAttack/HeartAttack_WhatIs.html
National Heart, Lung, and Blood Institute, National Institutes of Health
A heart attack occurs when blood flow to a section of heart muscle becomes blocked. A leading killer of both men and women in the United States, learn the symptoms and how acting fast can save your life and limit damage to your heart. If you think you or someone you’re with is having a heart attack, call 9–1–1 right away.