Some experts, however, said the results might be different depending on the formulation of one of the drugs used.
Prognosis for chronic heart failure is poor, with around half of patients dying within three to five years — a death rate similar to that of lung cancer.
In the largest such study to date, scientists estimated that those taking carvedilol, also known as Coreg in the United States or Dilatrend elsewhere, lived nearly 18 months longer than those taking metroprolol, another beta blocker.
The study, paid for by F. Hoffmann-La Roche and GlaxoSmithKline, marketers of carvedilol, and conducted by a committee of European heart failure experts, was presented Monday at a European heart failure conference in Strasbourg, France.
"Carvedilol's significant survival benefit could mean thousands of lives saved each year. The results will have a major impact on clinical practice," said lead investigator Dr. Philip Poole-Wilson, professor of cardiology at Imperial College in London.
However, Dr. Michal Tendera, European Society of Cardiology heart failure spokesman, gave a cautious interpretation of the results.
"This is most probably related to the drug, but it may also be due to the different formulation of the metroprolol used in this study compared to other studies of metroprolol," said Tendera, a professor of cardiology at Silesian School of Medicine in Katowice, Poland, who was not connected with the study.
The study used a short-acting generic metroprolol. Key research that established metroprolol as an effective beta blocker used the long-acting version known as Toprol XL and that research indicated the drug was as effective as carvedilol or other beta blockers, although there has never been a head-to-head comparison, Tendera noted.
"If you have a choice between the short-acting metroprolol and carvedilol, you'd definitely choose carvedilol, but if it's carvedilol or long-acting metroprolol, I don't think we have enough data to say that patients should be switched to carvedilol," he said.
Heart failure is a condition in which the heart is weak and cannot pump enough blood. The heart tries to compensate for its weakened pumping action by beating faster, which puts more strain on it.
Drugs known as beta blockers are commonly prescribed for the condition. They reduce the heart's tendency to beat faster.
Experts suggest there may be more than 10 million people with chronic heart failure in Europe alone and another 4.8 million in the United States, where the American Heart Association estimates that about 550,000 new cases are diagnosed every year.
The study, conducted in 15 European countries, involved 3,029 patients with all degrees of chronic heart failure. A total, of 1,511 people were given carvedilol and 1,518 got metroprolol, a generic drug. The patients were followed for almost five years.
By the end of the study, 512, or 34 percent of the carvedilol patients had died, compared with 600, or 40 percent, of the patients in the metroprolol group. The researchers estimated that the average survival was 1.4 years longer in the carvedilol group.
"There will be arguments about dose and formulation," Poole-Wilson said. "But the bottom line is we have compared two drugs and shown one is better than another."
The study could not determine why carvedilol was better, but scientists believe it could be because it works slightly differently.
Beta blockers block specific receptors — beta receptors — located on the heart cells, reducing the effects of chemical messengers that increase heart rate.
The body has two main beta receptors: beta 1 and beta 2. Some beta-blockers, such as metroprolol, block beta 1 receptors. Others, such as carvedilol, block both beta 1 and beta 2 receptors. Carvedilol is believed to block other activities that cause heart trouble.