Scientists claim that a side effect of the drug, paroxetine, is thought to be responsible for overcoming symptoms of heart failure, which occurs when the organ is too weak to pump sufficient blood around the body.
"This may open the way for a new class of therapies for a disease for which we lack effective interventions," said US lead researcher Dr Walter Koch, from Temple University Health System in Philadelphia.
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Paroxetine, used to treat depression, anxiety disorders and obsessive compulsive disorder (OCD), has been found to inhibit an enzyme that plays a crucial role in heart failure.
Previous research shows that heart failure in animals can be reversed by using genetic engineering to lower levels of the enzyme GRK2 (G protein-coupled receptor kinase-2).
In a new study, mice were given induced heart attacks which caused their hearts to fail over a period of two weeks.
When the heart failure was well developed, they were treated with paroxetine, fluoxetine (Prozac) - another widely used antidepressant - or an inactive dummy drug.
Only paroxetine restored heart function to near-normal levels, proving that its effect was unrelated to antidepressant properties shared with fluoxetine.
Paroxetine was also tested against the beta-blocker drug metoprolol, a standard treatment for heart failure.
"The beneficial effects of paroxetine were far greater than beta-blocker therapy," Dr Koch said.
GRK2 appears to be important for the unhealthy "remodeling" of a heart responding to damage caused by a heart attack. The maladaptive adjustments cause the heart to grow larger, weaker and less efficient.
One measure of heart efficiency, ejection fraction, shows how much oxygenated blood is pumped out by the heart's left ventricle chamber with each beat.
In the mice, ejection fraction fell from a pre-heart attack level of 70% to 35%.
After paroxetine treatment, it rose back up by roughly 30%.
The drug also caused pressure in the heart before each beat to return to normal and reduced heart weight and length, both of which increase in heart failure.
Dilation of the heart caused by patches of scar tissue was also greatly reduced when GRK2 activity was suppressed.
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Heart Attack Signs
It's Signs, Not Symptoms (01 of13)
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The Heart and Stroke Foundation makes the distinction of referring to the signs of a heart attack, as opposed to symptoms, because of the difference in the implied urgency between the two words, says Matthew Mayer, senior mission specialist with the organization. The word “symptoms” gives the impression that it’s something ongoing, maybe not as serious, Mayer says — like the symptoms of a condition versus the signs of an active health event. “Signs are more that this is happening... and something needs to be done.” (credit:Michaela Begsteiger via Getty Images)
Know The 6 Signs (02 of13)
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There are six signs that consistently show up during heart attacks, Mayer says, for both males and females. They are chest discomfort or pain, discomfort in other parts of the upper body, sweating, shortness of breath, nausea, and lightheadedness. Read on for more information about each sign. (credit:Rob Lewine via Getty Images)
Chest Discomfort (03 of13)
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Most of us know that chest pain is a clear sign that something is wrong, but the feeling in your chest that you have during a heart attack is not necessarily the kind of sharp pain you see depicted on television and in movies. For some people, it can feel like an uncomfortable pressure or squeezing, fullness, burning or a heavy feeling is also possible. But some people experience no chest pain or only mild discomfort during a heart attack — this is the most common sign, Mayer says. (credit:Nicholas Eveleigh via Getty Images)
Upper-Body Discomfort (04 of13)
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By the same token, you've probably heard that numbness or pain in your left arm is a sign of a heart attack, but that’s just part of the story. People having a heart attack might feel discomfort in their neck, jaw, shoulders, or upper back, Mayer adds. And as with the chest, for some it could be painful, and for others it could feel differently. (credit:laflor via Getty Images)
Other Signs (05 of13)
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Signs like nausea and lightheadedness can occur for a variety of reasons, of course, but many people who have a heart attack simply feel “weird” in some way. It’s better to be seen by a medical professional if you have one of or several of these signs, than to wait it out and risk heart damage. (credit:Colin Hawkins via Getty Images)
Hollywood Isn't Always Right(06 of13)
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Many of us have a mental image of what a heart attack looks like based on what we see on television or in movies: sudden onset, crushing pain, a hand clutching the chest. As the six main signs point out, that’s not everyone’s experience. (credit:Wavebreakmedia Ltd via Getty Images)
Discomfort vs. Pain (07 of13)
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A heart attack is not necessarily extremely painful. Discomfort can encompass a lot of different sensations, Mayer says, including sharp pain, soreness, numbness, pressure, squeezing, burning, or tingling. “What is one person’s pain is another person’s discomfort,” he says. The main takeaway is that the feeling, however you experience it, is unusual. (credit:Monica Rodriguez via Getty Images)
Men vs. Women(08 of13)
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More women than men die of heart attacks and stroke in Canada, Mayer says, and cardiovascular disease is the leading cause of death for women in this country. “Women are more likely to have the atypical signs,” he said of their experience with heart attacks. He says they are also more likely to describe feelings in their chest as discomfort and not pain. There is also research showing that women are slower to seek help when they do have a heart attack, he says, because they might be more focused on the health of their families and than their own. (credit:Blend Images - JGI/Tom Grill via Getty Images)
It's Not Always Sudden(09 of13)
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Always look into changes in your body that are outside your norm. That said, signs won’t necessarily appear suddenly or be very obvious. Lingering discomfort is a sign of a problem just as sudden pain is, and both should be investigated. “People need to be aware of how their body feels,” Mayer says. (credit:Jonathan Storey via Getty Images)
You Can Get Warnings Ahead of Time(10 of13)
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Sometimes people experience signs similar to those of a heart attack ahead of time, giving them a warning of trouble to come. For example, Mayer says, if you regularly experience tightness in your chest or shortness of breath during physical activity, that’s something you should discuss with your doctor. It could be a sign of blockages or artery narrowing, and getting it checked now might save you a heart attack in the future. (credit:Tim Robberts via Getty Images)
Know Your Risk Factors (11 of13)
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“People don’t take seriously how much their lifestyle comes into play with helping to deter a heart attack,” Mayer says. There are several lifestyle factors that increase your risk of heart attack, including smoking, high blood pressure, ethnic background (they are more common among younger people of South Asian, black, and Aboriginal backgrounds), a personal history of heart problems, family history of heart attacks before age 55, and age in general. Discuss your personal risk with your doctor, and know what to watch for when it comes to your heart health. The upside? Changing your lifestyle, for example, quitting smoking or reducing blood pressure, really can lower your risk of having a heart attack. (credit:Adam Gault via Getty Images)
Know That Time Buys Survival (12 of13)
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If you get to a hospital in time, the odds of surviving a heart attack are good, Mayer says. But time is of the essence, which is why it’s important to get checked out if you’re experiencing any of those six most-common signs. When you’re having a heart attack, he adds, the supply of blood (and therefore oxygen) to the heart is cut off. The result is muscle death, and the more muscle that dies, the higher the risk of complications if you do survive. “You heart cells don’t regrow,” Mayer says. “Once they’re damaged, they are damaged. If you delay and you begin to lose your heart tissue, there’s no getting that back.” And if you go into cardiac arrest, meaning that your heart stops beating, your brain is now being deprived of oxygen, and the question of surviving versus not surviving comes down to a matter of minutes. (credit:Oleg Moiseyenko via Getty Images)
Call 911(13 of13)
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At the end of the day, if you’re experiencing one or more than one of the six main signs of a heart attack, call 911 or your local emergency number and follow their instructions, Mayer says. Chest pain or discomfort is always a reason to call immediately, but the other signs should be taken seriously as well. It’s better to be a bit embarrassed for getting emergency help and finding out it’s nothing, than it is to wait. (credit:Blend Images/ERproductions Ltd via Getty Images)
Dr Koch said: "We believe this validates that GRK2 is a viable therapeutic target for heart failure and paroxetine is the starting point for a novel small molecule.
"We're looking at a totally new class of drugs for heart failure."
The therapeutic effect of paroxetine seemed to be long lasting, which was demonstrated when one one group of mice was treated for four weeks and then left untreated for two.
Co-author Dr Sarah Schumacher, from the Temple Centre for Translational Medicine, said: "The improvement was maintained. We think we reset the system. We stopped the vicious cycle of heart failure and restored basic function."
At present, symptoms of heart failure can be treated with drugs such as beta-blockers and angiotensin-converting enzyme inhibitors, but only a heart transplant can reverse the condition.
About half of people diagnosed with heart failure die within five years.
The concentrations of paroxetine used in the study were equivalent to those found in the blood of people treated with the drug for depression.
Dr Koch cautioned there could be no guarantee the effects in mice would also be seen in humans, but suggested that "at a minimum" physicians could consider prescribing paroxetine to heart failure patients who also suffered from depression.
"If you have to give these patients antidepressants, why not give them this one, which may improve heart function?" he said.
The scientists are now working on producing a derivative of paroxetine that can shut off GRK2 at lower doses without the antidepressant effect.
Dr Shannon Amoils, senior research adviser at the British Heart Foundation, said: "This interesting study shows that a drug, currently used as an antidepressant, can improve heart function in mice with heart failure apart from its antidepressant activity.
"The researchers found that paroxetene blocks an enzyme, called GRK2, which is known to be overactive in heart failure, and which contributes to the damaging changes in heart structure that occur in heart failure.
"However, the results need to be confirmed in humans. As paroxetine is already used in people, the next step is to see if it can be repurposed as a safe and effective treatment for heart failure in clinical studies."