Scientists at the University of Manchester believe that Viagra could be used to strongly suppress abnormal heart rhythms after a study of the drug in sheep

The British Heart Foundation funded study, published in Circulation Research- the leading journal in its field – could have important implications on the management of the condition on humans.

In female sheep, the drug – also known as sildenafil – was able to suppress an arrythmia called Torsades de Pointes within 90 seconds by reducing the frequency of irregular heart rhythms caused by abnormal handling of calcium.

It also reduced the probability of Torsades de Pointes, which can lead to sudden cardiac death. However, the team believe the drug could treat other arrythmias as well.

Cardiac arrythmias often follow a heart attack, or result from heart disease. Though often benign , they can cause symptoms including palpitations, breathlessness, fainting and sometimes sudden death.

Treatments such as beta blockers and implantable defibrillators exist, though are not always effective.

Working on isolated sheep heart muscle cells known as myocytes, the research team were also able to measure their calcium stores- as well as their electrical properties.

Although calcium is a key driver of the heart’s pumping action, its overload can be a root cause of arrythmias. Viagra was able to suppress the mechanism in the cell which causes calcium overload.

When a small amount calcium enters a myocyte, it triggers the Sarcoplasmic Reticulum (SR)- a calcium store – to release a larger quantity of calcium.

When there is heart disease, the SR can become overloaded with calcium which in turn makes the heart beat at the wrong time- when it is supposed to be resting between beats.

The mechanism is part of an enzyme pathway inside the cell involving PDE5 and activating a protein called protein kinase G which impacts on the arteries in the penis allowing blood to pump into it.

A similar mechanism exists around the muscle cells of the heart but has never been studied until now.

Dr David Hutchings is a lecturer at The University of Manchester. The paper’s lead author said: “Not only has this study demonstrated that Viagra has a powerful antiarrhythmic effect on living heart tissue, our cell studies have also uncovered the mechanism by which this happens.

“Though we studied the effect in sheep, we believe this discovery is likely to be relevant humans: the humans heart is a similar size to a sheep’s, as is its anatomy and associated electrical circuitry.

“So this discovery could one day unleash the potential for effective treatment on what can be a devastating problem.

“Clearly, anyone who has a cardiac arrythmia should not self-medicate and should consult their GP for advice on current treatment options.”

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