Doctors are turning to genetic testing in an effort to identify and prevent heart problems in patients who seem healthy but may be at risk because of a family history of heart diseases.

The tests, now taking off at a number of leading research hospitals, remain controversial amid debate over whether the information they yield will lead to improved outcomes and justify the additional cost.

A study, published in The Lancet last week about a healthy 41-year-old man with some family history of heart disease, illustrates how genetic testing can lead to early treatment and may stave off heart problems.

The patient—an engineer who invented a technology that can sequence the entire genome for less than $50,000—went ahead and sequenced his own genome, uncovering variants that prompted his cardiologist to prescribe blood cholesterol-lowering drugs called statins. The ability of the tests to predict who is at risk—and possibly lead to lifestyle changes, surgery or medication before the onset of disease—can make a significant difference in whether a patient ends up having heart problems.

Costs of gene testing are plummeting. A number of labs offer tests starting at a few hundred dollars. Cardiology clinics at academic research centers such as Stanford University in Palo Alto, Calif., and the University of Pennsylvania offer genetic testing.

These tests, nowhere near as in depth or expensive as whole-genome sequencing, search for alterations on small numbers of genes that research has shown are linked to certain increased risks. No one knows how many genes in all are involved in increased risk for heart problems. But because many researchers believe a $1,000 whole-genome sequencing test may be only three-to-five years away, they say it's critical to figure out now how to glean clinically useful information from these tests.

When assessing an individual's risk of heart attack and cardiovascular disease, cardiologists weigh factors including high blood pressure, high cholesterol, smoking, diabetes and lack of physical activity. In borderline cases, a detailed family history is helpful in determining whether to prescribe medicine immediately or continue monitoring. But some cardiologists question whether they get everything they need to know from family histories.

Self-reported information "is a very crude instrument and an incomplete way to assess inherited risk,'' says Daniel J. Rader, director of preventive cardiovascular medicine and lipid clinic at the University of Pennsylvania. A patient who reports having no family history of heart disease may still have inherited genes that greatly increase risk; the parent who transmitted the faulty gene may not have lived long enough for heart problems to have appeared. "Assessing genetic risk has the potential to provide information that cannot be gotten even from a good family history,'' says Dr. Rader, who in recent weeks has begun offering selected patients a test that looks for genetic variants linked to higher risk of heart disease.

Last spring, Stephen Quake, a bioengineering professor at Stanford University and a co-author of the Lancet paper, was in his office talking to a colleague, Euan Ashley, a Stanford cardiologist, and pulled up his whole-genome sequencing results on his computer. Dr. Quake pointed out alterations in a gene associated in the medical literature with hypertrophic cardiomyopathy, a condition that puts people at risk for sudden cardiac death. He mentioned his family's history of cardiovascular disease, including a cousin who died in his sleep at 19. Dr. Ashley recommended that he come to his clinic immediately for screening.

Dr. Quake, who rode his bike and swam regularly, ate right and didn't smoke, had a complete physical and screening tests including an ultrasound. He showed no signs of cardiomyopathy, but his blood lipoprotein level was elevated. Dr. Ashley said that according to guidelines for when patients should take statins, "if you input Steve's information, he falls just short.''

The men wondered whether the recommendation would change if Dr. Quake's whole-genome results were factored in. It took a team of researchers almost a year to create an algorithm that took into account all the known genetic data for 55 different conditions plus Dr. Quake's personal genetic data.

The risk analysis showed he has a greater-than-50% chance of developing obesity, type-2 diabetes and coronary artery disease. The researchers drew up a list of drugs that he should avoid based on genetic variations known to be linked to reactions with common medicines. The analysis indicated he would respond well to statins, and Dr. Ashley prescribed one.

Cardiologists who have studied the case say they aren't sure whole-genome sequencing was necessary to make that recommendation. Sekar Kathiresan, director of preventive cardiology at Massachusetts General Hospital and Harvard Medical School and a researcher whose work led to the discovery of gene alterations linked to early heart attacks, says he doesn't routinely get genetic tests for his patients. In the current clinical setting, he says, "often we don't exactly know what we would do differently based on the genetic test result."

For patients like Dr. Quake, Dr. Kathiresan adds, the only two medicines proven to reduce risk of a first heart attack are aspirin and statins. "His genetic test results weren't needed to make that clinical recommendation,'' Dr. Kathiresan says.

Dr. Quake says it wasn't family history, but the knowledge he had variants of genes linked to potentially serious heart troubles that sent him to the cardiologist's office. "It's one thing to know you have a little family history,'' he says. "It's another thing to know you have the mutation. It drives it home in a way that just knowing your family history doesn't.''

Despite his test results, Dr. Quake says he hasn't yet decided if he will follow Dr. Ashley's recommendation to take a statin. "I am still trying to figure out if I am ready to be a patient for the rest of my life,'' he says.