Ekaterina Bobrova is a former European champion who was part of the Olympic gold medal-winning Russian team at the 2014 Winter Olympics.
She told Russian media the positive test was "a big shock." Another Russian case last month saw cyclist Eduard Vorganov test positive.
Besides notable Russians, Swedish media reported in February that former world champion 1,500-meter runner Abeba Aregawi had tested positive for meldonium.
Two other cases involved Ukrainians competing in the winter sport of biathlon.
WHAT DOES IT DO?
Also marketed as mildronate, the website of the drug's Latvian manufacturer Grindeks says meldonium gives sufferers of heart and circulatory conditions more "physical capacity and mental function" - and a similar boost to healthy people.
Meldonium was banned because it aids oxygen uptake and endurance.
WHO TAKES IT?
Meldonium is most commonly used in Eastern European and ex-Soviet countries as a drug for people with heart conditions, but it's also offered for sale online.
There are also signs that a sizable minority of athletes were using before it was banned.
In October, the U.S.-based Partnership for Clean Competition, an anti-doping group, said meldonium was found in 182 of 8,300 urine samples from athletes as part of a study part-funded by the PCC.
HOW WAS IT BANNED?
The World Anti-Doping Agency monitored the effects and use of meldonium before announcing in September that it would be declared a banned substance from Jan. 1, 2016.
WADA declared the decision on its website more than three months before the ban, and it was also announced by the Russian anti-doping agency.
Sharapova said she received an e-mail from WADA linking to information that meldonium would be banned ahead of the 2016 season but did not read the information at the time.
Sharapova says she has been taking the drug for 10 years for numerous health issues.
