If you live in America, you probably know someone who has suffered from a heart attack. According to statistics, it’s the number one killer of both men and women in the U.S. Each year, about 735,000 Americans suffer a heart attack.

Most deaths from heart attacks occur because of ventricular fibrillation of the heart that occurs before the victim can reach an emergency room.

The good news is, those who reach the emergency room have an excellent prognosis. Survival from a heart attack exceeds 90%.

According to cardiologist Zi-Jian Xu, M.D, some people can notice subtle heart attack symptoms months before an actual event occurs.

So, here are 7 crucial symptoms that could occur months (or earlier) before a heart attack.

1) Extreme fatigue

Heavy fatigue that lasts for days, weeks or even months can signal heart trouble. This isn’t simply feeling “tired” but extreme fatigue that you’d usually associate with having a flu.

More than 70 percent of women in a National Institute of Health study reported extreme fatigue weeks or months before a heart attack.

Watch out for fatigue that occurs suddenly that can’t be linked to any other factors such as lack of sleep or illness.

2) Insomnia and anxiety

Heart disease may cause a decrease in oxygen levels which may trigger agitation and anxiety.

Two studies found a strong association between self-reported symptoms of extreme anxiety and a risk of heart disease.

Watch out for sleep problems or anxiety if you’ve never experience this problem before.

3) Shortness of breathe

When you can’t breathe deeply, you probably think the problem is your lungs. However, it can also occur from little oxygen in your blood from your heart. You might also feel light-headed and dizzy.

A study published in Circulation found that 40% of heart attack victims report shortness of breath 6 months prior to having a heart attack.

4) Excessive sweating

While sweating in hot weather or during physical activity is healthy, a study suggests that when individuals excessively perspire and begin experiencing discomfort in chest, arm, neck or jaw with no exertion, it could be a sign of heart failure.

Watch out for flu-like symptoms that can last longer than a week, or that come and go over a period of time.

5) Chest pain, heaviness or discomfort

Accorfing to Dr. Xu, this can occur months before a heart attack occurs. This is a somewhat typical symptom and can come and go at different times.

6) Feeling faint

Imperial College London researchers say that feeling faint or fainting can also occur up to a month before a heart attack in some patients. You also might feel dizzy at times.

Keep a watch out for this if the faintness can’t be linked to anything else, such as lack of water.

7) Irregular heart beat

This can usually last for 1-2 minutes and it might cause dizziness and fatigue. It often appears unexpectedly and can be either be an irregular heartbeat or increased heart rate.

Dr. Xu reminds us that it’s important not to ignore symptoms and wait until they become severe. If you have a concern, talk to your doctor. If heart disease is caught early, there are many lifestyle changes you can make to reduce your risk.