Nikolai Kulakov, director of the city's Royev Ruchei zoo, said the deaths are just a "wild coincidence," RIA Novosti reported.
Kulakov said autopsies of the animals showed one of the giraffes had a heart defect, low kidney function, a small heart and insufficient organ development. The second giraffe had no pathological problems, but video surveillance had picked up "some kind of conflict" between the two animals, he said.
That conflict could have led to stress that caused the death of the second animal, the director said.
A zoo spokeswoman said a commission comprised of park specialists and experts from the zoo's veterinary service had been formed to determine the cause of the deaths.