Professor Yacoub, who gave 10-year-old Matthew Poynter a new heart when he was just 16-months-old, was replying to accusations that his team at Harefield hospital wrongly failed to warn the baby's parents of the possibility of brain injuries.
Kevin and Linda Poynter, of Biggleswade, Bedfordshire are suing Hillingdon Health Authority in the High Court for damages on behalf of their severely disabled son.
They say they would have refused consent for the transplant had they been told of the risk, which tragically turned into reality.
The court has heard that Matthew, whose brain injuries occurred when he suffered a cardiac arrest during anaesthesia, was the only child to sustain brain damage among the 268 infants who have received new hearts at Harefield.
Prof Yacoub, a consultant cardiothoracic surgeon at the hospital in west London since 1968, gave evidence that the brain damage risk was less than one per cent. Parents were normally told of the risks of death or other common complications, but brain damage was not common.
He told Simeon Maskrey QC, for the Poynters, that he could not recall speaking to Mr and Mrs Poynter before Matthew's operation in December 1987, or whether he was told of their reluctance to consent to transplantation.
If he had been made aware that they were anxious to have all available information on potential disability, he would have felt under a duty to speak to them.
The judge asked Prof Yacoub what he would have told them.
Sir Magdi said he would have spoken of the risks and benefits, but would probably not have told them about the small risk of brain damage unless specifically asked.
"I did not consider then, and don't consider now, that serious brain damage is such a common condition that I ought to volunteer information," he said.
Questioned by Mr Maskrey, he said he was aware of the critical nature of Matthew's blood circulation before the operation, but this was not uncommon and he could not recall being particularly concerned.
He was aware that Matthew was considered incapable of receiving intravenous anaesthetic, but had no knowledge of the effect the halothane gas could have on his circulation.
"I am not an anaesthetist. That is an anaesthetic matter," said Prof Yacoub.
Mr Maskrey suggested that, in that case, he had been in no position to assess the risk of the baby suffering a cardiac arrest during anaesthesia.
Sir Magdi disagreed, saying he relied on experience. The anaesthetist was very experienced and it was up to him to decide on the drugs used.
Dr Richard Kirk, a former member of Prof Yacoub's team, denied telling Mrs Poynter that the hospital would have to consider seeking a court order if she continued to refuse consent to a transplant.
"I can't understand why I should have made such a statement to her," he said. If anything, he was "over-zealous" in giving information to parents about the risks, he said.
The hearing continues today with expert medical evidence and is expected to end tomorrow.Reuse content