Heart attacks occur when blood flow through the arteries to the heart (coronary arteries) is blocked for a time long enough to damage or kill a portion of heart muscle. Most, but not all, heart attacks cause symptoms, such as severe crushing chest pain, nausea, shortness of breath, or a feeling of impending doom. Some people with heart attacks die immediately, before they are able to receive medical attention. Others are admitted to hospitals and treated for their symptoms. Still others may live without ever recognizing that they had a heart attack. Past studies suggested that unrecognized heart attacks are generally common, representing as many as a third of all heart attacks, and are more common in women than men. It is not clear, however, exactly how frequently heart attacks go unrecognized in women with known heart disease.