Back in the Soviet Union's heyday, scientists tested meldonium on athletes in clandestine state-run labs, according to Ivar Kalvins, the Latvian chemist who invented the drug.
Kalvins asserts that decades ago he was shown the results of those tests, and they support what Sharapova has told the world: Meldonium is medicinal, not performance-enhancing. "Most athletes should be on this drug," he said. "It protects the heart."
But he doesn't have the actual studies to support his claims.
"These trials were never published," Kalvins said, citing the secrecy of the era. He said the Soviets wouldn't even give him -- the inventor of the drug -- a copy of the results.
There's no use in trying to find the studies now, he added. Most of the people who were involved back in the 1980s "are not with us in this world, and the rest, for sure will not speak about things," Kalvins told CNN. "It is Russia still."
Decades later, Kalvins' statements leave top U.S. doctors calling them -- to use a polite word -- baloney.
'Pseudoscience and unsupportable claims'
Cardiologists interviewed by CNN said if Kalvins can't show the data, then there's no way of knowing if his drug does protect athletes' hearts from damage due to overexertion, as he said in an interview
"If you don't show your data, your claims might as well disappear into thin air, because they're not credible," said Dr. Aaron Baggish, an assistant professor of medicine at Harvard Medical School.
According to Dr. Steven Nissen, a former president of the American College of Cardiology, Kalvins' statements in that interview were "filled with pseudoscience and unsupportable claims. It was almost humorous it was so over the top."
Nissen, chairman of the department of cardiovascular medicine at the Cleveland Clinic, said there's no reason an elite athlete's heart needs protecting in the first place.
"She's 28 years old!" he said, referring to Sharapova. "The idea that her heart needs protecting -- it just doesn't make any scientific sense. The argument doesn't stand up to scientific scrutiny."
Baggish, the cardiologist for the U.S. soccer and rowing teams, agrees.
"The prevailing science says the vast majority of athletes can push their heart to the limit and come out stronger," said Baggish, who directs the Cardiovascular Performance Program at Massachusetts General Hospital. "They can do as much activity as they want and not end up with heart failure."
Several companies sell melodium under various names. In a statement, the original and major manufacturer of the drug, a Latvian pharmaceutical company called Grindeks
, said the drug "can stop tissue damage in the case of ischemia," or insufficient blood flow to the heart.
Kalvins, chairman of the scientific board of the Latvian Institute of Organic Synthesis, said the Soviet-era tests showed meldonium helped decrease the amounts of fatty acids going to the heart, which he said "is safer for the heart."
He added that he hasn't made any money off the drug since 2005, and even then he only made "a little."
Dr. Paul Thompson, director of cardiology at Hartford Hospital and former president of the American College of Sports Medicine, also said he was dubious about the assertions that meldonium is helpful for athletes' hearts.
"It's very easy for the person who invented the drug to say it protects athletes' hearts. That's what you call a conflict of interest," he said. "If I invented the drug, I'd say that, too."
Sharapova: One drug for many illnesses
At her March 7 press conference
, Sharapova, who moved to the United States when she was 7, said she took Mildronate, a brand name for meldonium for various illnesses.
"I was given this medicine by my doctor for several health issues that I was having back in 2006. I was getting sick a lot. I was getting the flu every couple of months. I had irregular EKG results as well as indications of diabetes with a family history of diabetes," she said.
"(Mildronate) made me healthy, and that's why I continued to take it," she added.
Mildronate's manufacturer, Grindeks
, does not include diabetes or influenza on its list of uses for the drug.
The drug has been approved in several former Soviet republics, such as Russia and Latvia, but not by the U.S. Food and Drug Administration or the European Medicines Agency, the European equivalent of the FDA.
U.S. doctors interviewed for this article said they weren't familiar with the drug but said they were highly doubtful one medicine could treat all the complaints Sharapova mentioned.
"There's not a medication in the world that I know of that's going to treat that constellation of symptoms," Baggish said.
Nissen said only Sharapova and her doctor can explain why she was taking meldonium for so many different problems.
As for irregular electrocardiogram results, Mildronate does treat cardiac conditions, according to the manufacturer's website. But it's unclear what, if any, cardiac condition Sharapova has.
At her press conference, the tennis player didn't supply any more details beyond that she'd had the irregular EKG. Her attorney, John Haggerty, referred questions to Mary Jane Orman, a spokeswoman for IMG Tennis, which manages Sharapova. She declined to comment on the player's medical history.
Irregular EKG results can mean nothing, cardiologists told CNN, especially for athletes.
"We've known for decades that athletes' hearts are different than the hearts of normal people," Baggish said. "If you compare them to sedentary people, their results fall outside the limits of normal, but that doesn't mean anything is wrong."
For example, studies show between 30% and 50% of athletes will have abnormal EKGs compared with the rest of the population because they have left ventricular hypertrophy, he said. That means the left side of their heart is large, which isn't surprising given how much they exercise.
"The heart is a muscle. And so, like other muscles, it gets bigger if it is worked hard over time," according to the Cleveland Clinic's website
Sharapova is not alone
Sharapova may have put melodium on the map, but she's hardly the only athlete to have taken the drug, which the World Anti-Doping Agency
banned starting at the beginning of the year.
An analysis last year of 8,300 urine samples taken at doping control sessions revealed that 182 contained the drug, according to the Partnership for Clean Competition
"There is an alarmingly high prevalence of meldonium use by athletes in sport," the report concluded.
At last year's European Games -- when meldonium was not on the banned list -- 66 out of 762 athletes tested positive for the drug, according to an article in the British Medical Journal.
Meldonium was particularly popular among certain types of athletes. Nearly a third of the canoeists and kayakers and a little more than a quarter of the gymnasts in the report tested positive for the drug.
Does meldonium enhance athletic performance?
According to the British Medical Journal article, meldonium might enhance athletic performance.
There's some evidence that the drug may benefit exercise performance in rats, according to the study authors, and in humans there have been reports that the drug improves blood flow to the heart and increases tolerance to stress.
"Consequently, the use by athletes could potentially result in enhanced personal performance and a shortening of the recovery period after physical activity," the authors wrote.
They added that the "widespread use" of the drug suggests "there is some benefit being observed which is potentially perpetuating its use among athletes."
Grindeks, the pharmaceutical company, said in a statement that "meldonium cannot improve athletic performance" and is therefore not a doping agent and should not have been banned by the World Anti-Doping Agency.
But Nissen, the cardiologist at the Cleveland Clinic, said he wonders if perhaps it's all in the athletes' heads.
"The placebo effect is very powerful," he said. "I can imagine how this plays out in the athletic world, where you're operating at the 99th percentile of human performance. Someone says, 'I can give you something that's going to make you a little bit better.' It's very tantalizing to try it."