Oscar Pistorius was transferred from prison to a local Pretoria hospital after experiencing chest pains, according to The Associated Press.
There were South African reports that Pistorius - serving six years for the 2013 murder of his girlfriend Reeva Steenkamp - suffered a heart attack in jail, but they turned out to be false.
"He's fine now," Pistorius' spokesman Johan van Wyk told the AP.
Pistorius spent time in hospital last year for cuts to his wrist, sustained after a fall in his cell.
The 30-year-old Paralympic champion has served one year of his sentence.