Comedian and broadcaster Sir Michael Palin is to have surgery to fix a "leaky valve" in his heart.
The Monty Python member discovered a problem with his mitral valve - a small flap that stops blood flowing the wrong way around the heart - five years ago.
It had not affected his general fitness until earlier this year, he said.
"Recently, though, I have felt my heart having to work harder and have been advised it's time to have the valve repaired," he wrote on his website.
"I shall be undergoing surgery in September and should be back to normal, or rather better than normal, within three months."
According to the NHS, a leaking mitral valve - known as mitral regurgitation - can cause dizziness, breathlessness, tiredness and chest pain, and can potentially lead to an irregular and fast heartbeat, high blood pressure and heart failure.
The 76-year-old has cancelled a book tour scheduled for October to promote his North Korea Journal, a spin-off from his recent Channel 5 documentary about the country.
Earlier in July, he finished another tour to promote his non-fiction book about HMS Erebus, a ship that voyaged to both the Arctic and Antarctic in the 19th Century.
Palin was one of the six-strong troupe who revolutionised comedy in the 1960s and 70s, and later became known for his globetrotting TV documentaries.
He recently told the Too Old To Die Young podcast: "I have realised that I have reached the age of 75 without feeling in any shape or form like someone of 75 - mentally, certainly.
"Physically, I think I'm a little bit slower perhaps than I used to be. But I'm still fairly fit. I'm probably fitter, and certainly look after myself better, than when I was in my mid-20s."
He also owns a Bafta Award for best supporting actor, which he received for starring in the 1988 film A Fish Called Wanda.