Oscar is doing well under the circumstances, his father Henke Pistorius says.
The Paralympic athlete was kept in Kalafong Hospital in Atteridgeville, Pretoria overnight for observation after experiencing chest pains on Thursday morning.
“He has been discharged and is back in the facility,” Logan Maistry, spokesperson for the department of correctional services, told AFP.
Henke told YOU Oscar had previously had “bad colds” and it was not clear whether this was a reason for the severe pains in his chest.
Several tests have been performed on Oscar since Thursday and “all the tests were negative”, said Henke.
The 30-year-old is serving a six-year prison sentence for the murder of his model girlfriend, Reeva Steenkamp, in February 2013.
Oscar has been behind bars for the murder of Reeva Steenkamp, since July 6 last year. He argued that he thought she was an intruder.
He was transferred from the Kgosi Mampuru II prison to the Atteridgeville priso