The 33-year-old announced he'd be leaving football in an emotional press conference on Wednesday morning.
Aguero struggled to breath during a game against Alaves in October and would never play for the club again.
Roberto Peidro, who has treated Aguero since 2004, has revealed the Argentina international has a small scar near his heart after a previous cardiac issue.
"He has a very small scar in his heart area which is less than a millimetre which is why it sort of short-circuits and causes those arrhythmias," Peidro told Argentine radio per The Mirror.
"What was done using a catheter was to burn that area where the arrhythmias were coming out.
"We think it's going to work very well and solve the problem but our advice is that he shouldn't do high-performance sport that involves an important degree of mental and physical stress several hours a day."
The procedure is said to help irregular heartbeats, something Aguero was diagnosed with at a young age.
Peidro was quick to stress Aguero will be able to live a normal life, despite not being able to continue his career.
He also believes the small scar was caused by a virus - but NOT Covid-19 or the vaccine.
"The most common scenario is that the small scar found is produced by a virus he's suffered at some point in his life and wasn't ever detected," Peidro continued.
"But it has nothing to do with Covid or the Covid vaccine.
"I spoke with no-one before Sergio's retirement announcement because this formed part of my duty of professional secrecy, but he allowed me to speak to the media and explain things.
"It was a shared decision for him to quit professional football. He was very anxious and when I saw the test results the first thing I said was: 'If you were my son, I would advise you to go this way.'"
Aguero spent nine years at Manchester City and became the club's record goalscorer with 260 in all competitions.
He won six League Cups, five Premier League titles and the FA Cup during his time in England.
Last summer saw him move to Barcelona, for who he made four appearances, scoring once.
Aguero broke down in tears at the Camp Nou saying his final farewells, explaining it was for his own personal health.
Featured Image Credit: PA Images & Barcelona
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