Young athletes diagnosed with certain heart problems may for the first time be eligible to play competitive sports under new recommendations from the nation’s two leading heart groups.

The scientific statement, issued Monday by the American College of Cardiology and the American Heart Association, says athletes ages 12 to 25 with a type of irregular heartbeat called long-QT syndrome and those with a pacemaker or implantable cardioverter defibrillator, or ICD, may now be allowed to play competitive sports.

Currently, there are more than 460,000 athletes in the NCAA and more than 7.8 million students who play high school sports. Douglas Zipes, M.D., co-chaired the committee that wrote the new guidelines and said sudden cardiac death among young athletes is rare. One study estimated that roughly 66 athletes ages 13 to 25 die from sudden cardiac arrest each year.

Although more young non-athletes die from cardiac arrest, young competitive athletes are at greater risk for sudden cardiac death  if they have an underlying heart problem — a problem that is almost always undiagnosed, said Barry Maron, M.D., director of the Hypertrophic Cardiomyopathy Center at the Minneapolis Heart Institute Foundation and co-chair of the statement’s writing group.

“If there wasn’t any reason to be restrictive, there’d be no reason for guidelines,” Maron said.

But there are now some exceptions, such as for young athletes with long-QT syndrome, a rare, inherited condition that affects the heart’s electrical system and can lead to cardiac arrest. Players with the condition can compete as long as they don’t have symptoms or have been symptom-free for at least three months.

The change comes a decade after the last set of recommendations and is based on new research that suggests a lower risk of cardiac arrest for people with long-QT syndrome than previously thought.

The guidelines recommend athletes with long-QT stay hydrated and avoid drugs, such as certain antidepressants and medications for attention deficit hyperactivity disorder, that could cause an abnormal heart rhythm. Athletes should also consider getting a personal automated external defibrillator, or AED, a portable device that can shock the heart back to a normal rhythm during cardiac arrest.

The new recommendations also allow young athletes with ICDs  or pacemakers to play competitive sports if they are symptom-free and do not have structural heart problems. However, those who depend on the heart devices to regulate their heartbeat should avoid contact sports, the guidelines say, because the device could dislodge or become damaged.

Even given the new recommendations, doctors might be hesitant to allow an athlete with an ICD to play a contact sport, said Tim Neal, a certified athletic trainer for 36 years and a member of the National Athletic Trainers Association.

That’s despite a 2013 Yale University Medical School study that found many athletes with ICDs can engage in vigorous and competitive sports without physical injury or failure to stop a dangerous heart rhythm, despite shocks that may occur during sports.

Andrew Lovell, a freshman running back at Methodist University in North Carolina, may be the first college football player in the nation to compete with an ICD. The team’s physician and the university’s certified athletic trainers collaborated with his cardiologist, Nicole Cain, M.D., who signed a university release allowing Lovell to play.

Experts agree the guidelines involve careful decision-making between doctors and athletes.

“The physician’s medical judgment is the last call,” said Zipes, a professor of medicine at Indiana University School of Medicine in Indianapolis.

Brian Hainline, M.D., chief medical officer for the NCAA, said his organization is not involved in eligibility decisions for individual colleges but instead issues science-based recommendations to help guide decision-making.

“There is no ‘line in the sand’ that absolutely defines clearance or lack thereof to play,” Hainline said.

The recommendations otherwise remain largely unchanged from a decade ago. Still restricted from competitive sports are athletes with hypertrophic cardiomyopathy, or HCM, a thickening of the heart muscle. Often inherited, it is the most common cause of sudden cardiac death in athletes, according to the statement.

HCM is also among the most common health problems that prevent students at NCAA schools from participating in competitive sports, Hainline said.

Even doctors can’t predict all the time which athletes with heart problems are at risk for sudden cardiac arrest, said Zipes. So the guidelines recommend having players and coaches know how to perform CPR and use an AED, which should be available at practice, in the training room and on the playing field.

Past recommendations that erred on the side of caution did so because doctors didn’t have a good understanding about these diseases and what might happen to young athletes who had them, Zipes said.

“But as we’ve learned more about some of these problems,” he said, “we’ve now liberalized their athletic participation.”