BOSTON, SEPT. 2 -- -- Using balloons to force open clogged heart arteries immediately after heart attacks does not appear to provide significant health advantages, a study concludes.

Researchers said this technique works just as well if done a week or more after the heart attack.

The research did not attempt to assess whether the procedure, known as balloon angioplasty, improves survival when used in combination with clot-dissolving medicines. However, one expert said the work raises questions about whether the procedure helps those who suffer heart attacks.

Dr. Thomas J. Ryan of Boston University Medical Center called the findings "surprising and important." However, authors of the latest study "may, in fact, have provided the first indication that, as a treatment for acute myocardial infarction, the high-flying balloon of angioplasty is losing some of its air," Ryan wrote in an editorial published with the study in Thursday's New England Journal of Medicine.

The study by the Thrombolysis and Angioplasty in Myocardial Infarction Study Group was conducted on patients who received a clot-dissolving drug called tissue plasminogen activator for their heart attacks. Doctors performed angioplasty immediately on 99 patients and waited seven to 10 days to do the procedure on 98 others. During a follow-up, no significant difference was found in the status of patients' hearts in the two groups.