CHICAGO - Death rates and heart failure in hospitalized heart-attack patients have fallen sharply in just six years, most likely because of better treatment, the largest international study of its kind suggests.

The promising trend parallels the growing use of cholesterol-lowering drugs, powerful blood thinners, and angioplasty, the procedure that opens clogged arteries, the researchers said.

"These results are really dramatic because, in fact, they're the first time anybody has demonstrated a reduction in the development of new heart failure," said lead author Keith Fox, a cardiology professor at the University of Edinburgh in Scotland.

The six-year study involved nearly 45,000 patients in 14 countries who had major heart attacks or dangerous partial artery blockages. The percentage of patients who died in the hospital or who developed heart failure was nearly halved from 1999 to 2005.

And the heart-attack patients treated most recently were far less likely to have another attack within six months of being hospitalized when compared with the patients treated six years earlier - a sign that the more aggressive efforts of doctors in the last few years were working.

There have been other indications that better treatment of heart patients has been saving lives, but not on a scale as large as this international study, the researchers said.

"It's much more dramatic than we expected, in the course of six years," Fox said.

The new study follows landmark research results in March that showed angioplasty was being overused on people who had chest pain but were not in immediate danger of a heart attack. But this popular procedure, which typically uses stents to keep an unclogged vessel open, is still a powerful tool for saving those who are having a heart attack or are at high risk of one, results showed.

Patients for the study enrolled between July 1999 through December 2005 and were followed for up to six months after hospitalization. Besides the United States, they were in hospitals in Argentina, Australia, Austria, Belgium, Brazil, Canada, France, Germany, Italy, New Zealand, Poland, Spain, and the United Kingdom.

Among the findings:

4.6 percent of the heart-attack patients died in the hospital in 2005, vs. 8.4 percent in 1999.

Heart failure developed in 11 percent of heart-attack patients in 2005, compared to nearly 20 percent in 1999.

2 percent had subsequent heart attacks in 2005, compared with 4.8 percent in 1999.

Improved outcomes also were found in those with partial blockages, which include less severe heart attacks.

The researchers said these marked improvements were probably a "direct consequence" of new practices that followed updated guidelines from key organizations of heart doctors in the United States and Europe.

The study "is the first report of what's actually going on in the real world," said Joel Gore, a co-author and cardiologist at the University of Massachusetts Medical Center.

Recommendations in those guidelines include quick use of aspirin or more potent blood thinners; beta blockers to reduce the damaged heart's oxygen needs; statins to lower cholesterol; ACE inhibitors to relax blood vessels; and angioplasty to open blocked vessels soon after hospital arrival.

Use of each of these treatments climbed during the study and in some cases more than doubled. For example:

85 percent of heart patients studied got cholesterol drugs in 2005 vs. 37 percent in 1999.

78 percent got potent blood thinners, including Plavix, in 2005 vs. 30 percent in 1999.

53 percent had quick angioplasty in 2005, compared with 16 percent six years earlier.

The study appears in today's Journal of the American Medical Association.

It was funded by a grant from Sanofi-Aventis, maker of several heart drugs, including Plavix and ACE inhibitors. Fox and several other authors reported getting fees and grants from Sanofi and other drugmakers.

Steven Nissen, former president of the American College of Cardiology and a Cleveland Clinic heart specialist, said the study did not prove the recommended treatments were saving lives - but he suspected that was the case.

"I really am encouraged that those things that appear in our guidelines are being used by physicians around the world," Nissen said.

American Heart Association spokesman Sidney Smith said the results were "exactly what we would hope would happen from the major efforts in this area over the past decade."

"The tragedy," Smith said, "is that too many patients delay before coming to the hospital."