Treating the bacterial infection with a common antibiotic seems to reduce the risk of a second heart attack, British researchers said in a report published in Monday's edition of the American Heart Association journal Circulation.

Dr. Sandeep Gupta and his colleagues at St. George's Hospital Medical School in London measured levels of antibodies to an organism called Chlamydia pneumoniae in 213 patients who had had heart attacks.

Some patients with the highest antibody levels were given the antibiotic azithromycin.

Gupta and his colleagues then documented which patients went on to experience other heart problems that required treatments such as bypass surgeries, angioplasties or heart drugs. Some patients died or had second heart attacks.

The researchers found that the patients who had received antibiotics had no greater risk of developing further heart problems than did patients who never had been infected with the organism.

``This is the first prospective study in which patients with evidence of being infected (by the bacterium) are more prone to heart attack than those who are not affected,'' said Dr. Valentin Fuster, director of the Cardiovascular Institute at Mount Sinai School of Medicine in New York City.

The findings might have important implications for preventing the onset of heart problems, but a bigger study is needed to confirm that, Gupta said.

Gupta said he did not know if the presence of antibody meant the patients had an ongoing infection or if the infection had occurred in the past.

Inflammation caused by a variety of germs has been implicated in the development of heart disease. Scientists believe that such infections somehow play a part in damage to arteries, leading to complete blockage of blood flow and a heart attack.

Gupta said the association between high levels of Chlamydia antibodies and coronary artery disease is still unclear.

Fuster said the findings ``may open a door to a new understanding'' about how infection could combine with other risk factors to contribute to heart attacks. It is possible, he said, that further study could show that the bacterium is as important a trigger for heart attacks as cigarette smoking.

In a report in Circulation last December, researchers from the University of Washington found evidence of Chlamydia pneumoniae infection in fatty tissue taken from the carotid arteries that supply blood to the head. The tissue was removed because it was blocking the arteries and impeding blood flow to the brain.