Speaking to Sky Sport at the Gran Gala del Calcio in Milan, the Scotland international addressed his condition directly.
"I'm fine, the heart operation was something I'd already planned to do with the club for a while," McTominay said.
"We'd already talked about it in pre-season, I'll be out for a few weeks."
Napoli have confirmed the 29-year-old will undergo a cardiac arrhythmia ablation procedure to correct a mild, benign irregular heartbeat, with the club expecting him back after the upcoming international break.
Asked about working under new head coach Massimiliano Allegri, McTominay said the fundamental approach at the club remained unchanged despite the managerial switch.
"We have a new coach, but the mentality is always the same: try to win," he said. "Allegri is a great coach, who has already won a lot in his career. I get on well with him."
The Scot has been a central figure for Napoli since his move from Manchester United in 2024, contributing significantly to the club's Serie A title win in 2025.
On his contract situation, with speculation continuing over a possible extension, McTominay said there had been no fresh discussions and downplayed the significance of the topic for now.
"I don't know, there haven't been any new talks," he said. "The important thing today is the pitch, not the renewal. I still don't know when, or if, I'll renew my contract with Napoli."
McTominay's procedure comes at a difficult moment for Napoli, who lost their most recent match against Como with the midfielder substituted in the second half after what Allegri had initially described as blister problems, before the club later confirmed the true reason for his discomfort.
His scheduled absence is expected to cover around a month of action, including matches in Serie A and the Champions League, before a possible return in October.
The procedure itself, known as pulsed field ablation, is a minimally invasive technique that treats irregular heartbeats by delivering short, high-voltage electrical pulses to targeted areas of faulty heart tissue.
Medical staff have stressed the condition is relatively common among elite athletes and is not expected to have any lasting impact on his career.
McTominay has made 82 appearances for Napoli since joining from Manchester United, scoring 27 goals and establishing himself as one of the club's most important performers during their title-winning campaign under previous management.