“A player from the men's rugby sevens national team admitted the results from his A sample and rejected the opportunity to test his B sample,” the RRF added in a statement.
“A sportswoman from the women's rugby sevens team says she has not taken any illegal substances and has asked for her B sample to be tested.”
Meldonium was added to the World Anti-Doping Agency's list of banned substances on Jan. 1.
Eight other Russian sportsmen and women have been found to have taken meldonium including former world number one tennis player Maria Sharapova.
The others are biathlete Eduard Latypov, cyclist Eduard Vorganov, figure skater Ekaterina Bobrova, speed skater Pavel Kulizhnikov, short-track speed skaters Semion Elistratov and Ekaterina Konstantinova and the volleyball player Alexander Markin.
Rugby sevens will be making its Olympic debut in Rio de Janeiro in August.
Original source: Russian rugby duo have taken meldonium