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Sometimes drugs that are designed to treat a certain disease can unexpectedly work for other conditions as well. According to a new study from the University of Manchester, Tadalafil — a drug from the same class as the famous Viagra, which meant to treat erectile dysfunction — seems to slow or even reverse heart failure.

Heart failure is a chronic disease that requires lifelong management. It occurs when the heart is too weak to pump enough blood through the body. When cells aren’t supplied with enough oxygen and nutrient-rich blood, the body can’t function normally, resulting in fatigue, shortness of breath, and coughing. When the condition sets in, even mundane activities such as walking or climbing stairs can become difficult.

At first, the heart tries to compensate for its inadequate pumping rate in several ways, including enlarging, developing more muscle, pumping faster, narrowing the blood vessels, and diverting blood supply away from less important tissue. These measures only temporarily mask the problem since heart failure worsens in time until the compensation mechanisms no longer work. These measures also explain why it usually takes years for a patient to realize that their heart has stopped functioning properly. Often, the diagnosis comes too late — the disease has five-year survival rates lower than most common types of cancer.

Most treatments for heart failure are ineffective, which is why the new study from the University of Manchester is so exciting.

Human trials and epidemiological studies showed that Tadalafil, known by the brand name Cialis in the US, might effectively treat heart failure. Professor Andrew Trafford and colleagues performed a new study that investigated this relationship more closely. The team administered the drug to sheep with heart failure, whose condition was induced by pacemakers. Shortly after the first dose, the progression of the disease was stopped and, in some cases, the drug even managed to reverse the effects of heart failure. The dose received by the sheep was similar to the dose humans take in order to treat erectile dysfunction.

“This discovery is an important advance in a devastating condition which causes misery for thousands of people across the UK and beyond,” said Professor Trafford.

“This study provides further confirmation, adds mechanistic details and demonstrates that Tadalafil could now be a possible therapy for heart failure,” he added.

Tadalafil is known to block the activity of an enzyme called Phosphodiesterase 5 (PDE5S), whose role is to regulate how tissue responds to hormones like adrenaline. Trafford and colleagues found that in sheep affected by heart failure, the drug triggers a cascade of chemical reactions that restores the heart’s ability to respond to adrenaline. For instance, breathlessness due to heart failure is caused by the inability of the heart to respond to adrenaline and this symptom disappeared in the sheep that were given Tadalafil.

The drug also increased the heart’s ability to pump blood around the body. However, despite the promising results, the researchers advise people that they shouldn’t self-medicate and ought to always consult with their doctors before taking new medication.

“Viagra-type drugs were initially developed as potential treatments for heart disease before they were found to have unexpected benefits in the treatment of erectile dysfunction. We seem to have gone full-circle, with findings from recent studies suggesting that they may be effective in the treatment of some forms of heart disease—in this case, heart failure,” said Professor Metin Avkiran, Associate Medical Director at the British Heart Foundation.

The findings appeared in the journal Scientific Reports.