In a report to the 10th Conference on Retroviruses and Opportunistic Infections, Dr. Nina Friis-Moller, a researcher at the Copenhagen HIV Programme in Denmark, said persons taking combination treatment of anti-HIV drugs have a 26 percent increased risk of suffering a heart attack each year they remain on medication.

"While we are concerned about this, the absolute risk of heart attacks remains low and should be balanced with the known beneficial effects of highly active antiretroviral therapy (HAART) in the prevention of HIV-related complications," said her colleague, Dr. Jens Lundgren, director of the Copenhagen HIV Programme at Hvidore University Hospital.

The researchers reviewed data collected on 23,468 HIV-infected patients in Europe, Australia and in the United States. Among those patients, 126 suffered heart attacks, 36 of which proved fatal.

However, other researchers questioned whether the increase in heart attacks seen in the study reflects the role of the medication or the impact of the disease. HIV infection creates an inflammatory state within the body. Such inflammation has been linked to the cascade of events leading to coronary artery disease and heart attacks.

Dr. Priscilla Hsue, a clinical research fellow in cardiology at the University of California, San Francisco, used high resolution ultrasound devices to image the carotid arteries -- the main arteries to the neck -- to see if they narrowed over the years. The "carotid intima-media thickness" is known to predict the risk of developing heart disease, she said in her presentation.

Hsue enrolled 106 subjects into the study and scrutinized not only their neck arteries but also a host of other factors, including duration of disease, the patients' ages and their overall health.

She reported carotid intima-media thickening, as it is called, progressed most rapidly in patients who carried classical heart disease risk factors: increasing age, higher levels of low density lipoprotein, or LDL, cholesterol -- the "bad" cholesterol -- and high blood pressure.

Hsue also looked at levels of CD4-positive cell counts in these patients. CD4-positive cells are a marker for the effectiveness of the patient's immune system. The cells are attacked during HIV infection. Low CD4-positive cell counts -- below 200 -- reveal advanced HIV infection. Hsue said accelerated progression of intima-media thickening occurred if a patient ever had a CD4-positive cell count below 200.

She suggested her data indicate it was the impact of disease, rather than the impact of certain medications, that was increasing the risk of heart disease.

In a third study, Dr. Judith Currier, adjunct associate professor of medicine-infectious diseases at the University of California, Los Angeles, also studied narrowing of the carotid arteries. She compared patients infected with HIV who were taking protease inhibitor HAART regimens with HIV patients not on HAART regimens that included protease inhibitors. She also compared both groups with non-HIV control subjects.

The 134 patients in the groups were matched for other risk factors for heart disease, including smoking, high blood pressure and high cholesterol.

Her preliminary result: After two years, she could not detect any significant differences in the groups. However, Currier said the study is ongoing and future developments could show different outcomes.

Dr. Constance Benson, professor of medicine, University of Colorado Health Sciences Center in Denver, noted questions surrounding whether it is the drugs or the disease that results in coronary disease remain controversial.

"However, Dr. Currier's ongoing work appears to have the best chance of sorting that out," she said.

"I think the increase risk in heart disease with HAART regimens containing protease inhibitors is real," said Dr. Scott Holmberg, senior medical epidemiologist at the Centers for Disease Control and Prevention in Atlanta. But he added that these same drugs are valuable in keeping patients with HIV infection alive and functioning normally. Other combinations of antiretroviral drugs -- which fight retroviruses such as HIV -- that do not contain protease inhibitors also are effective in controlling the disease, he said.

"What makes more sense is to get the patients with HIV infection to decrease their modifiable risk factors such as to getting them to stop smoking," Holmberg said. "More than 50 percent of HIV-infected individuals smoke cigarettes. That is an enormous smoking rate compared to the rest of the U.S. population. They should also be encouraged to modify their diets to reduce cholesterol levels."

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