Nearly every 34 seconds someone in the United States has a heart attack, according to the American Heart Association. In fact, heart disease is the number one killer of both men and women in the U.S.

But that's where some of the similarities end.

A study of heart attack patients finds that women are more likely than men to show up at the hospital without the classic chest pain symptoms of heart attack. The study also shows that women are more likely to die in the hospital following a heart attack. The study was published today in the Journal of the American Medical Association.

Researchers used data from more than 1 million patients in the National Registry of Myocardial Infarction, a large national database of heart attack patients from about 1,600 acute care hospitals in the United States. Women comprised 42% of the patients in the study. The database is sponsored by Genentech, Inc., which makes an anti-clotting prescription drug, but that product was not discussed in this study, which focused on sex, age, and heart attack symptoms of hospital patients.

The heart is a muscle that requires oxygen to fuel it's constant beating. When the blood flow bringing oxygen to the heart is impaired or cut off by a blockage, a heart attack occurs.

Recognizing that a patient is having a heart attack and beginning treatment quickly is vital to preserving the heart. Without blood flow and oxygen, the heart muscle begins to die, forming scars that damage and impair heart function, and producing serious long term health problems.

"Patients without chest pain/discomfort tend to present later, are treated less aggressively, and have almost twice the short-term mortality compared with those presenting with more typical symptoms of [heart attack]," the study authors write.

While the symptoms of heart attack typically include chest pain and discomfort, likened to having an elephant sitting on your chest, previous studies have shown that women often have less typical heart attack symptoms including dizziness, shortness of breath, upper back pressure, extreme fatigue, nausea, or pressure in the lower chest or belly, according to the American Heart Association.

Among the study participants, women presenting with heart attacks were older than men, averaging 74 years compared to 67 years for men. Women were also less likely to have chest pains or discomfort -- 42% of women had no chest pains, compared to only 30.7% of men without chest pains.

Age was also a factor for symptoms: Younger women were less likely to have chest pain symptoms compared to men of the same age, although that difference equalized among the sexes with increasing age. In-hospital deaths for women was 14.6%, compared to 10.3% for men.

While the authors note the sex-based differences in heart attacks are largely unknown, they cite research suggesting that estrogen in women may have a protective effect on their hearts. The study concludes that more research - specifically looking at differences in symptoms between the sexes and age groups - is needed to better identify heart attacks that may have atypical symptoms.