Pinochet, who is accused of murder and torture during his 1973-1990 rule, was rushed to hospital on Sunday.
He is expected to stay in hospital for at least a week.
Brink of death
Marco Antonio Pinochet, the retired general's youngest son, said his father had been on the brink of death in the moments after the heart attack.
|"I'm surprised the general has recovered so well in less than 24 hours"|
Hugo Gutierrez, lawyer for two people who disappeared after the 1973 coup
"If he had arrived [at the hospital] five minutes later, the doctor tells me, he would have died," he told a local radio station, rounding on sceptics who accuse his father of faking ill health to avoid prosecution for human rights abuses and fraud.
Pinochet's former foreign minister and lawyer, also defended his friend against allegations that his health problems are a hoax.
"That's absurd, no one would expose himself to surgery for something fake. He's 91 and he has a large inventory of high risk ailments. I know for a fact that he was on death's door," Hernan Felipe Errzuriz, told Al Jazeera.
But the suspicions will not go away. Hugo Gutierrez, a lawyer for two people who disappeared after the 1973 coup in which Pinochet took power, also cast doubt on his quick recovery.
"I'm surprised the general has recovered so well in less than 24 hours," he said.House arrest
Last week, Pinochet was ordered to remain under house arrest over the murder of two of President Salvador Allende's bodyguards during the coup.
But on Monday a panel of judges on the Santiago appeals court ruled he should be freed on bail.
Pinochet has previously avoided standing trial because his lawyers convinced the supreme court was unable to defend himself because of a "mild dementia," the only condition that exempts a defendant from trial in Chilean courts.
Supporters and opponents of the former president have gathered outside the hospital since he was admitted.
More than 3,000 people died in political violence during his 17-year rule and about 28,000 were tortured. Many more fled into exile.
Many loyalists lost faith in Pinochet when it was revealed in 2004 that he hid about $28 million in foreign bank accounts. He has been charged with tax fraud and courts are investigating the origin of the funds.