A team of Harvard-affiliated doctors has been awarded a $1-million grant to study a treatment preventing strokes in patients suffering from heart conditions.

Investigators at the Massachusetts General Hospital (MGH) received a five-year grant from a division of the National Institutes of Health last July 1 to explore the benefits and possible side effects of "warfarin," a potent anticoagulant (anticlotting) drug.

The MGH doctors said they hope to determine which patients suffering from a heart condition called atrial fibrillation (AF) should receive the drug. AF is a disorder of the heart's upper chambers, or atria, that doctors say causes 15 percent of all strokes in the United States.

Strokes result when blood clots tear free from the heart and lodge in an artery in the brain. The affliction is the third leading killer in the United States, behind heart disease and cancer.

"The objective of the study is to determine if the benefits of warfarin outweigh the risks due to complications such as bleeding," said Dr. Robert A. Hughes, director of the MGH's Anticoagulant Therapy Unit.

Hughes and Dr. J. Philip Kistler, a neurologist heading the Stroke Service, will lead the interdepartmental study.

Warfarin has been given to some subgroups of AF patients' over the past 30 years with varying degrees of success. There has been no well-designed study with absolute proof to convince doctors that the drug really works, Hughes said.

The program will admit 350 people, averaging 65 years of age, over the next three years. Half of the participants will receive warfarin with the remainder serving as a control group.

Hughes's biggest worry is that it may be difficult to recruit patients to participate in the program.

"Most people find it anxiety-provoking to be part of a study. Their doctors will have to convince them they can be a real benefit to medicine and society," he said.

Although warfarin seems to reduce the incidence of stroke in AF patients, Hughes said the risks for users are not to be dismissed.

"Anyone who goes on [warfarin] may have a hemorrhage," he said. The alternatives are between "suffering a stroke in the control group or possibly bleeding from warfarin, and it's difficult to predict the severity of either one," he added.