Viagra appears to reduce the effects of hormonal stress on the heart by 50 percent

Viagra works by helping genital blood vessels expand to maintain an erection, but more recently, it has also been used as a treatment for pulmonary hypertension.

However, Viagra has been thought to have no direct effect on the heart.

"Unlike what was previously thought, drugs like Viagra, they can in fact alter heart function," said lead researcher Dr. David Kass, a professor of medicine at Johns Hopkins. "It alters it particularly when the heart is stimulated by hormones.

"The report appears in the Oct. 24 online edition of Circulation. Earlier research by Kass's team found that Viagra blocked the short-term effects of hormonal stress in the hearts of mice.

They also found that, in mice, Viagra prevented and reversed the long-term cardiac effects of chronic high blood pressure.

In addition, Kass' group found that, in mice, Viagra reversed the negative effects on heart muscle weakened by heart failure and enlargement, a condition called hypertrophy.

In the current study, 35 healthy men and women with no signs of heart disease received two separate injections of dobutamine over three hours. Dobutamine increases heart rate and pumping strength. Between injections, the patients were given Viagra or a placebo.

Then they all were given a second dobutamine injection. After the first injection of dobutamine, the force of heart contraction increased 150 percent in all the patients.

However, in the group treated with Viagra, the increased heartbeat was slowed by 50 percent.

"Viagra puts a brake on the effect of dobutamine," Kass said.

"Viagra reduces the stimulation of the heart so that the contraction of the heart was less strong.

"Kass noted that his group is starting a clinical trial to see if Viagra, can be effective in patients with heart failure. "

If you gave a drug like Viagra not just acutely, but chronically, you might be able to improve heart function and reduce the chronic stress response in patients with hypertrophy," he said.

One expert believes that Viagra may have a role to play in the treatment of heart failure.

"This research may lead to the development of a new use of Viagra in the treatment of diseases such as hypertension, hypertrophy and heart failure, where beta-adrenergic activity is enhanced following neurohormonal stimulation," said Rakesh C. Kukreja, a professor of medicine, physiology, biochemistry and emergency medicine and the Eric Lipman chair of cardiology at Virginia Commonwealth University Medical Centre.

"These studies are complementary to the expanding new role of Viagra and other relatively safe PDE-5A inhibitors as powerful cardioprotectants," he added. However, another expert was more cautious.

"Viagra has a potential, but the crucial studies will be in actual patients with cardiac conditions, and on other medications to see if cardiac stress will be minimized with sildenafil," said Hrayr S. Karagueuzian, a senior research scientist in the Division of Cardiology at Cedars-Sinai Medical Center, in Los Angeles.

" I am not going to buy it on its face value," Karagueuzian said. "Let's see what happens. We simply do not know if the balance of the effect of Viagra will end up on the benefit or the deleterious side."

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