WHEN George Skouras, an investment manager in New York, turned 52, he decided to go for a complete physical exam. He felt perfectly healthy, but wanted to know if there was anything to worry about.

So he went to a specialty clinic for tests. Among them were heart scans. The news was not good. Mr. Skouras had a plaque buildup in his coronary arteries, partly obstructing two.

What, he wondered, should he do? He knew his cholesterol level was a bit high. But he hesitated to take statins, drugs that can lower cholesterol levels, concerned that side effects might emerge over decades. And though he worries that statins are not completely safe, most cardiologists cite large, long-term studies finding that the drugs are rarely risky and that benefits, for the populations studied, are indisputable.

His quandary, heart specialists said, reflects the difficult questions that a new era in heart disease assessment has produced: do new tests, like heart scans, work to people’s benefit? How much testing for heart disease makes a difference, and what tests should people have? What should you do if you have a test and it shows something you did not expect?

The answers, as often happens in medicine, depend on whom you ask.

Mr. Skouras consulted several experts, including Dr. Peter Libby, the chief of cardiovascular medicine at the Brigham and Women’s Hospital in Boston. Dr. Libby says he is hearing from more patients like Mr. Skouras. They undergo tests for heart disease, but once they have the results, they are not sure what to do.

Nearly everyone agrees on the basics. Adults should know their cholesterol, blood-sugar and blood-pressure levels and should keep them within national guidelines. It is often reasonable to try dieting and exercising, but if that fails, most people should take prescription drugs.

If everyone took those steps, that alone could make the heart attack rate plummet, says Dr. Daniel Levy, the director of the Framingham Heart Study, a federal study of the population of Framingham, Mass. Dr. Levy said the study indicated that nearly every heart attack from age 50 to age 95 could have been prevented if people had their blood pressure, blood sugar and cholesterol under control at age 50 and did not smoke. Yet, he noted, only 5 percent of the nation’s 50-year-olds do this.

But the testing question gets murky after that. Some, like the United States Preventive Services Task Force, a federally sponsored panel of experts in primary care and prevention, says that most people should take only basic tests. “The message we are trying to get across is that more testing is not always beneficial,” said the panel’s chairman, Dr. Ned Calonge.

The concern is that seemingly innocuous tests will give false-positive results, which lead to more tests and even treatments, when there was nothing wrong to begin with.

When it comes to people like Mr. Skouras, who know they are at increased risk of heart disease — remember, his cholesterol level was too high — Dr. Calonge wonders what more tests can possibly reveal. The only thing Mr. Skouras can do to protect himself against a heart attack is to lower his cholesterol level, advice he already has.

Dr. Daniel Rader, who directs the lipid program at the University of Pennsylvania School of Medicine, said he might be faced, for example, with deciding how to advise a 40-year-old man with a family history of premature heart disease, and whose LDL cholesterol is 125, at the high end of normal. Should this man take a statin to lower his cholesterol further?

“No one knows,” Dr. Rader said. The guidelines say he does not need the drug. Yet, Dr. Rader says, his family history is worrisome. Many people like him will have a heart attack.

Dr. Rader, like other heart specialists, said he often turned to more tests to assess how great the person’s risk really is. For example, he may test for blood proteins whose presence in elevated levels can indicate increased heart attack risk. Dr. Rader said he also he might suggest heart scans, like those Mr. Skouras had.

Mr. Skouras decided to see how far he could go with diet and exercise instead of taking statins. He was not fat, but he lost 16 pounds, reducing his LDL cholesterol level by 30 percent, to 140. That, though, is not as low as Dr. Libby would like.

So Mr. Skouras remains troubled. As he sees it, it’s all a matter of probabilities — the chance that a statin will prevent a heart attack for him personally, which no one can tell him for sure, versus the chance that a statin will turn out, after decades of use, to have been worse than nothing for him personally. And that, of course, is also unknown.

“The frustrating thing,” Mr. Skouras said, “is no one can really tell you cause and effect — that if you do this, this is what you will get.”