Spot the warning signs of 4 dangerous conditions

We rarely think life-threatening conditions, like a heart attack, can happen to us. And we tend to miss signs that such conditions are brewing. "You think, 'I'm too young' or 'too healthy' for it to be true, and you can ignore important symptoms," says Dr. Emily Lau, a cardiologist at Harvard-affiliated Massachusetts General Hospital.

Protect yourself by learning the warning signs of the following conditions, and taking action if you recognize them.

1. Heart attack

A heart attack occurs when something blocks blood flow to a part of the heart muscle. It can be fatal. The typical symptom is extreme pain or pressure in the middle of the chest. Chest pain that comes and goes, especially with exertion, is one early warning sign. But other symptoms also can be warning signs, such as new shortness of breath; fatigue; nausea or vomiting; or sudden pain in the abdomen, back, jaw, or shoulder, even without chest pain. "Women are more likely to have these other symptoms in addition to chest pain, but men can also have them," Dr. Lau says.

How can you tell it's a heart attack and not something else? Ask yourself two questions: is the symptom new, and is it recurring or not going away? "For example, if you could walk up a flight of stairs yesterday without any issues, and now the same level of activity is very hard for you, then something is wrong," Dr. Lau says. Or if you experience a pain in your abdomen, back, jaw, or shoulder when you exert yourself, especially if it recurs or isn't going away, contact your doctor promptly.

2. Stroke

A stroke occurs when blood flow to the brain is blocked or a blood vessel in the brain bursts. It can be fatal. A major stroke can cause sudden difficulty speaking or understanding someone, numbness or weakness on one side of the body, blurry vision, dizziness, or a severe headache. Any one of those warrants an immediate call to 911.

In some cases, the first warning of an impending major stroke might be a ministroke (transient ischemic attack, or TIA). It has the same symptoms as a major stroke, but they last only briefly and are easy to brush off. For example, you might lose vision in one eye for a minute, and maybe think it's because you were looking at your smartphone screen too long. But a TIA is often the harbinger of a bigger stroke. The symptom may go away, but the next episode could cause permanent damage. "If a stroke symptom of any kind occurs suddenly, even if it goes away, call your doctor's office immediately," Dr. Lau says.

3. Atrial fibrillation

Atrial fibrillation (afib) is the name for rapid, abnormal contractions of the heart's upper chambers (the atria). Instead of squeezing in concert, the atria quiver, which can make the blood inside them pool and form clots. The clots then can travel to the brain, heart, or other parts of the body and cause life-threatening damage.

Many people with afib don't have any symptoms. "But you might detect afib if you experience palpitations — a feeling that your heart is beating unusually rapidly or irregularly, even when you're resting. You might also feel faint or experience sudden fatigue," Dr. Lau says. "And some people recognize it by wearing smart watches that track heart rhythms. The technology isn't perfect, but it is pretty good at recognizing afib."

If you suspect you're having afib symptoms, write down how often they occur, and when, and see your doctor as soon as possible.

4. Pulmonary embolism

A pulmonary embolism occurs when a blood clot forms in a leg, then travels upward and lodges in a lung. The clot can reduce your body's supply of oxygen-rich blood and damage the lung. Sometimes it's fatal: "It can cause blood to back up in the heart, and even cause your heart to stop," Dr. Lau says.

The main symptoms of a pulmonary embolism — extreme fatigue and shortness of breath, chest pain, or passing out — will probably get your attention. But you might not connect other symptoms to a pulmonary embolism. For example, it can cause flu-like symptoms such as a cough, fever, dizziness, wheezing, or heart palpitations. If you have blood clots in the deep leg veins (called deep-vein thrombosis, or DVT), you might have pain, swelling, or redness in one leg. "If you're not sure if you have symptoms, think of your risk factors. Have you been sitting for long periods? Are you on a medication that can cause clotting? Do you have a family history of DVT? All of these can cause blood clots in the legs. If you have both suspicious symptoms and these risk factors, call your doctor promptly," Dr. Lau says.

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