ORLANDO, Fla. — Say you've had a heart attack and your insurer offered you free medicines to help prevent another one. Doctors did that in a major study and were stunned to find that only about half of patients took them.

Those who did suffered fewer heart-related problems and saved $500 on average for health care over roughly a year. And it didn't cost the insurer more; in fact, costs were trending lower because of fewer hospitalizations. 'People don't get as sick, and it's people getting sick that costs the most money,' said Dr. Lonny Reisman, an author on the study and chief medical officer for Aetna, one of its sponsors.

Aetna plans to start offering some of these drugs for free or with a reduced co-payment to some heart attack survivors and is researching whether to do so for other chronic conditions such as diabetes and chronic lung disease, Reisman said.

'A drug only works if it's taken,' said Dr. Eric Peterson of Duke University. 'Adherence in America is miserable,' and only 10 percent of patients in this study were taking all medicines they should one year after a heart attack, said Peterson.

It was proposed and led by Dr. Niteesh Choudhry of Brigham and Women's Hospital in Boston, who presented results Monday at an American Heart Association conference in Florida. They also were published online by the New England Journal of Medicine.

The study enrolled 5,855 Aetna plan members who had a drug plan as part of their benefits and were going home from the hospital after a heart attack. They were 53 years old on average, and three-fourths were men. Preventive medicines were offered free to 2,845 patients and prescribed with the usual co-pays for the rest.

Roughly one year later, compliance with taking medicines, measured by how many filled prescriptions, ranged from 36 percent to 49 percent, depending on the drug, and improved only 4 percent to 6 percent in the group that had no co-pays.