Having a pacemaker fitted has not stopped veteran wildlife broadcaster David Attenborough climbing trees, he says.
Sir David, 87, who has also had knee replacement surgery, said his insurers insisted on him having the device fitted.
"I had to go to Australia and the insurance said they wouldn't insure me to go on a long flight unless I had something to monitor my heart to make sure it didn't do funny things," he said.
"So they give you this thing, it's called a pacemaker.
"And all it does, if your heart suddenly decides it's going to skip a beat or something, it kicks in.
"And if it doesn't, it doesn't. And I don't think it has."
But, appearing on Friday night's The Jonathan Ross Show Christmas Special on ITV1, he said the operation had not held him back.
"I've just come back from Qatar and before that was in Rome and I'm just off to Borneo," Sir David said.
"I only do it because it's fun. I'm not as good at climbing trees as I was, but I've been up in a tree recently."
