What is trimetazidine, the drug Russian skater Kamila Valieva tested positive for before the Olympics?

An uncommon heart medication is at the center of an Olympic doping scandal that nearly sidelined a dynamo Russian figure skater before the Court of Arbitration for Sport ruled Monday that Kamila Valieva could compete in the short program of the women’s single skating competition.

International anti-doping officials met Sunday to review the case of Valieva, the 15-year-old star of the Russian Olympic Committee’s figure skating team who tested positive for trimetazidine before the start of the Beijing Olympics. The heart disease medication, which is not approved in the United States, is considered a performance-enhancing drug and banned by the World Anti-Doping Agency.

CAS on Monday upheld the Russian Anti-Doping Agency’s decision to lift a Feb. 9 provisional suspension it imposed against Valieva the day before, CNN reported. The court said Monday that it based its ruling on “exceptional circumstances” — among other issues, Valieva is considered a “protected person” because she is a minor — under the World Anti-Doping Code.

Here’s what to know about the drug trimetazidine.

Trimetazidine is a medication used to improve blood supply to the heart among people with the coronary heart disease angina. The drug causes the blood vessels to dilate, allowing the heart to work more efficiently for a longer duration of time, said Deepika Thacker, a cardiologist at Nemours Children’s Hospital in Delaware.

Trimetazidine may be used to treat adults with angina, a type of chronic chest pain. The drug is not approved for use in the United States, but is used in some European countries. Even in countries where it is approved for use, trimetazidine is not typically a first-choice medication because other, more common medications, such as beta blockers are more effective with fewer side effects.

Potential side effects include nausea, vomiting, and gastrointestinal discomfort. Parkinson’s disease-like neurological side effects, such as tremors, have also been reported.

“There’s no legitimate reason for a 15-year-old girl to be on it,” Thacker said. “Children overall don’t get coronary heart disease, and among the small percentage of kids who do, this is not a first-line medication that would be used because of the side effects.”

When heart disease does occur among children, it is most often a structural problem present at birth, Thacker said. Adults, meanwhile, develop heart problems after years of poor eating, lack of exercise, and other unhealthy habits that contribute to plaque buildup in the arteries — problems often treated by a combination of medication, lifestyle change, and possibly surgery.

What’s more, a teenager would probably not be able to compete as an elite athlete, as Valieva does, if they had this type of heart problem, Thacker said.

Trimetazidine has been on the World Anti-Doping Agency’s list of banned substances since 2014. Unlike some other banned substances, trimetazidine does not give users an immediate boost in physical strength and energy. However, the drug improves the heart’s efficiency, which could allow an athlete to train harder and longer, giving them an edge in a future performance.

“It’s not going to give you an adrenaline drive and make you run faster, but by improving the metabolism of the heart and improving blood supply to the heart, it improves your endurance long-term,” Thacker said.