Jackson Muamba, a 17-year-old basketball player from northern New Jersey, died of a heart attack on the court a few years ago.

Recently, Brad Merriman, a 15-year-old basketball player from Indiana collapsed and died during practice.

Autopsies later revealed that these young people suffered heart attacks, a rarity for youths. But the American Medical Association warns that young adults, in high school and college, already are at risk for heart disease.

The heart problems of young adults sometimes remain undetected because younger people may not show symptoms and are otherwise healthy.

According to the AMA Web site, cigarette smoking, high blood pressure, high cholesterol and obesity contribute to heart disease among young adults. Family history is another factor but one that is out of a person’s control.

About 250,000 adults die of sudden cardiac arrest every year in the United States. These sudden deaths are defined as untimely and unexpected, according to the Medline Plus Web site.

Young athletes with heart problems are at higher risk because heart attacks are sometimes spurred by physical activity. Hypertrophy, known as an enlarged heart, can be particularly dangerous if patients overexert themselves.

An enlarged heart can be detected by physical examination, x-ray or imaging tests. The condition occurs for different reasons, including the thickening of the heart muscle or muscle damage.

Cardiomyopathy is a disease in which the heart muscle becomes inflamed and causes the heart to function inefficiently. This condition is sometimes brought on by viral infection. Hyper cardiomyopathy occurs when the muscle mass of the left ventricle is larger than usual.

The most frequent form of an enlarged heart is dilated cardiomyopathy, in which the cavity of the heart is enlarged and stretched.

The AMA offers advice for young people seeking to minimize the risks of heart disease. AMA writer Linda Kollar suggests that teens and young adults should get their blood pressure checked at least once a year.

Young people should choose food low in fat and cholesterol, Kollar wrote.

If it grows in the ground, the food has no cholesterol, Kollar wrote. If it has feet, fins, wings or claws, the food contains cholesterol.