Russian star figure skater Kamila Valieva tested positive for trimetazidine a month before she won the team event gold medal at the 2022 Winter Olympics. Here's what you need to know about the banned drug:

Trimetazidine, known as TMZ, is a drug used to treat angina and other heart-related conditions. It works by increasing blood flow to the heart and limiting rapid swings in blood pressure. The drug is not approved for use in the United States.

"If you're in a highly exertional sport, where you're using a lot of energy and you're putting your heart under significant stress, it certainly could help your heart function better theoretically," said Dr. Kelly Johnson-Arbor, a medical toxicology physician at MedStar Georgetown University Hospital.

It has been on the World Anti-Doping Agency's (WADA) list of prohibited substances since 2014. It is currently categorized as a "hormone and metabolic modulator," which is illegal for athletes to use both in and out of competition.

It is believed that TMZ can improve physical efficiency, especially in the case of endurance sports, although opinions vary on how long-lasting the effect could be.

TMZ is usually taken once or twice a day, and easy to detect in tests as a synthetic drug.

Russian athletes are no stranger to the substance. At the 2018 PyeongChang Olympics, Russian bobsledder Nadezhda Sergeeva was disqualified two days before her race after testing positive for the drug.

One of the most high-profile cases involving trimetazidine is that of Chinese star swimmer and Olympic gold medalist Sun Yang, who was penalized with suspension in 2014 after testing positive for the drug. Sun said he was prescribed the drug to treat his chest pains.

TMZ is another example of a metabolic modulator like meldonium, which has featured in allegations against the Russians for doping.

At the PyeongChang Games, Russian curling athlete Alexandr Krushelnitckii handed back his bronze medal after testing positive for meldonium.

Russian tennis player Maria Sharapova was banned for 15 months after testing positive for meldonium in 2016