The discovery could prompt the discovery of drug treatments to help those at highest risk.

This protein it produces plays a role in the growth of blood vessels. but too much of it may increase stroke risk.

Writing in the journal Nature Genetics, the scientists said people with certain forms of a gene called PDE4D may be most at risk.

Proteins from a similar “family”, called phosphodiesterase (PDE), are linked to other illnesses, such as asthma, inflammation and even erectile dysfunction.

This suggests that it may be possible to develop a drug to block the effects of the gene - the breakthrough impotence drug Viagra already works by targeting another member of the PDE family.

Solveig Generic online pharmacy viagra
and colleagues at a company called deCode Genetics in Reykjavik believe this gene is associated with an increased risk of stroke.

They carried out DNA tests on over 1,700 people in Iceland, half of whom had suffered strokes.

The Icelandic population is generally regarded as the best testing ground for geneticists.

This is because the gene pool is relatively pure. Unlike most other countries, there has been little alternative health treatment womens
since the first Vikings arrived almost 1,000 years ago.

Scientists working on this latest study say they have identified genetic differences between those people who have had strokes and those who have not.

These differences centre on the gene PDE4D, located on chromosome 5.

They have found that three different isoforms of the gene were expressed at lower levels in people who had strokes.

Isoforms are groups of proteins that are produced by a gene.

They also found different generic viagra fast shipping
of genes in regions of chromosome 5 flanking the PDE4D gene in people who had strokes.

It is already known that this gene provides the coding which enables a protein called a phosphodiesterase to work.

Stroke risk

But the Icelandic scientists believe that too much of it may increase the risks of atherosclerosis - furring up of the arteries.

This causes the arteries to narrow, which can trigger a stroke.

“We propose that PDE4D is involved in the pathogenesis of stroke, possibly through atherosclerosis, which is the primary pathological process underlying ischemic stroke,” the scientists said.

They believe that blocking the protein in people with these 50mg generic viagra problematic forms of the PDE4D gene could protect them against stroke.

There are already drugs available to do this. These so-called phosphodiesterase inhibitors are used to treat asthma, inflammation and erectile dysfunction, with Viagra probably the best known.

However, much further study is needed before these drugs could be used to treat people who may have a high risk of having a stroke.

Viagra, for one, has potentially serious side effects if taken by men with underlying health problems.

The drug, used by millions of men, slowed the increase in the strength of heart erectile dysfunction drugs
by half.

The Johns Hopkins University study, published in Circulation, found the drug acted as a “brake”.

However, UK heart experts warned men with heart conditions should talk to their doctor about taking the drug to ensure they use it safely.

Mixing this drug with other heart medicines or taking it if you have angina without advice from a health professional or GP can be dangerous for heart patients Dr Charmaine Griffiths, British Heart Foundation

Viagra, also known as sildenafil, helps men with erectile impotence by making genital blood vessels expand in order to maintain an erection.

The Johns Hopkins team have previously shown Viagra can block the short-term effects of hormonal stress in the heart in mice.

But it had been thought to have little direct effect on the human heart.

Impotence product

This study looked at 35 men and women, with an average age of 30 and no previous signs of coronary artery disease.

They were all given an injections of an adrenaline-like chemical called dobutamine, which increases heart rate and pumping strength in the same way as emotional or exercise stress, or heart failure.

They were then randomly assigned to either take 100mg of Viagra or a dummy pill before receiving a second injection. Heart function was measured before and after each jab.

After the first injection of dobutamine, the force of heart contraction increased by 150% in both groups.

In the dummy pill group, the same effect was seen after the second injection.

However, in the group treated with Viagra the increased heartbeat was slowed by 50%, resulting in a smaller increase in blood flow and blood pressure generated by the heart in response to chemical stimulation.

No adverse side effects on the heart were seen.

Viagra helps maintain erections by blocking the action of an enzyme which prevents the relaxation of blood vessels in the penis.

The same enzyme, called cause of male impotence 5 (PDE5A), is also involved in the breakdown of a key molecule, cyclic GMP, which helps control stresses and limit heart erectile dysfunction drugs
.

Heart warning

Professor David Kass, the cardiologist who led the study, said: “Sildenafil effectively puts a 'brake' on chemical stimulation of the heart.”

He added: “Knowing more about the effects of sildenafil on heart function will allow for safer evaluation of its use as a treatment for heart problems.

“Until now, it was widely thought that drugs like sildenafil had no effects on the human heart and that its only purpose was vasodilation in the penis and the lungs.”

He said further studies should be carried out to investigate Viagra's immediate and long-term effects on the heart.

Dr Charmaine Griffiths, from the British Heart Foundation, said: “Viagra has been a real advance in treating impotence, which affects nearly half of men between 40 and 70 years old.

“The findings that Viagra affects blood pressure is not surprising - before it was known as a successful treatment for impotence, it was actually being researched for lowering effects on blood pressure.”

But she added: “If you have a heart condition you should check with your doctor before taking Viagra.

“Mixing this drug with other heart medicines or taking it if you have angina (heart pain on exercise) without advice from a health professional or GP can be dangerous for heart patients.”