Maria Sharapova failed a doping test and admitted to using an endurance-enhancing drug

Sharapova, 28, said she’d been using the drug, meldonium, for the past 10 years. That’s a great deal of her professional career — Sharapova turned pro in 2001.

“I had been taking this medicine for the past 10 years, but on 1 January this became a prohibited substance, which I did not know,” she told reporters at a press conference in Los Angeles on Monday.

Meldonium is an anti-ischemic drug that is meant to treat angina, heart attacks, and heart failure. Anti-ischemic drugs prevent the deprivation of oxygen to the heart, brain, or other organs. WADA noted that the drug has potential “cardiac effects.”

But according to the journal Drug Testing and Analysis, meldonium can enhance an athlete’s performance by increasing “endurance performance of athletes, improved rehabilitation after exercise, protection against stress, and enhanced activations of central nervous system (CNS) functions.”

WADA began monitoring the drug in 2015.

Though Sharapova has been dealing with injuries (legs and shoulder) over the past few years of her career, there hasn’t been a reported mention of her battling a chronic heart condition. On Monday, Sharapova revealed that she had a magnesium deficiency and a history of diabetes, which prompted her to take the drug.