BOSTON: The damaging effects of a heart attack may be reversible, say researchers who have successfully used drugs to boost new heart tissue and blood vessel growth.

Treating the hearts of rats that had experienced simulated heart attacks, the team found the repaired hearts beat as well as undamaged hearts even after several months.

"This is a dramatic recovery," says Felix Engel, pediatrician at the Children's Hospital in Boston who led the study. "A human with this kind of heart muscle damage would be dead."

Under normal conditions, when blood flow is prevented from reaching the heart during a heart attack, the tissue dies, forming irreparable scar tissue. To re-grow the damaged areas in rats, Engel and colleagues used two drugs: one that overcomes a natural inhibitor of cell division within the heart; and one that encourages blood vessel growth.

The researchers studied 120 rats, some with heart attacks simulated by permanently closing off one of the coronary arteries that feed the heart muscle. Rats that received both drugs showed the greatest improvements.

Yibin Wang, a physiologist at the University of California, Los Angeles, US, who collaborated with Engel on a preliminary study, praised the new work but questioned some of its claims.

"The bottom line of this study is great," Wang said, "they found a way to break the barrier of cardiac regeneration. But it's very challenging to claim all of the benefits they observe are truly due to regeneration."

Wang noted that heart function began increasing just one day after the heart attack - too soon, in his opinion, to be attributed to regeneration.

He suspects the damaged cells never died, but were protected by the drugs, which were applied at the same time as the simulated attack.