The anti-impotence drug Viagra could be a good treatment for heart failure, US researchers believe.
Viagra increases blood flow
A Johns Hopkins team told Nature how they found it effectively treats enlarged hearts - a common feature of heart failure - in mice.
Cardiologists said it was reasonable to presume it would have such an effect.
Viagra was initially designed to be heart drug until scientists found a useful spin off effect on the blood vessels of the penis.
It works by expanding blood vessels to improve blood flow, similar to other angina drugs.
There have been concerns about whether it is safe for men with heart disease on particular medications that work in the same way.
Doctors are told not to prescribe Viagra (sildenafil) along with these drugs called nitrates.
But it appears to be safe in other heart patients.
In the latest study, Dr David Kass and colleagues looked at the effect of Viagra in mice with enlarged hearts.
In humans, this can occur with high blood pressure, which causes the heart's muscular wall to thicken and the heart can eventually fail.
The mice that received Viagra had smaller hearts despite their high blood pressure compared with mice that did not receive the drug.
In a second experiment, Viagra was found to reverse heart enlargement, or hypertrophy, in mice that already had heart failure.
Dr Kass said: "This study shows that sildenafil can make hypertrophy go away."
They plan to study the effect in humans and believe it could lead to new treatments for heart failure.
But Professor Peter Sever, of the National Heart and Lung Institute at Imperial College London, said there were already effective drugs for heart failure and that Viagra's action was not unique.
Dr Ian Banks of the Men's Health Forum said: "There has always been this feeling that it benefits the heart."
He said it could not be prescribed in this way because it is not licensed for treating heart conditions.
The British Heart Foundation said more studies were needed before the potential benefits of Viagra could be fully understood.
A spokeswoman said: "If you have a heart condition you should check with your doctor before taking the drug.
"Although there are many causes of cardiac hypertrophy, a main one is high blood pressure.
"If you do suffer from high blood pressure, try to reduce the amount of salt you eat, drink only a moderate amount of alcohol, and take lots of exercise."