There are moments when your life changes over the length of a single word. For example, you might remember that particular time you heard the word “pregnant”. Or maybe “divorce” or “congratulations” or “guilty”. And maybe you remember the silence that followed and how it had a new weight to it. As if the silence were saying: “Look, if I’m expected to follow words like that, I’m going to need a bit more respect around here.” That’s how it was for me last October. I didn’t get to choose my life-changing word, of course. If I had, I doubt I would have gone with “prolapse”.

“It looks like a prolapse.”

“Yes, the valve is prolapsed and there’s severe regurgitation.”

“Due to the prolapse. All right, Mr Webb? Nearly done.”

An echocardiogram – an ultrasound of the heart – is in progress. The setting is a hospital and the time is that far-off era when we imagined hospitals to be places full of sick people having their own bespoke emergencies rather than sick people having one national emergency. More normal times, you might say – when we had the spare attention to be interested in all the deadly medical conditions that you can’t get from a doorknob. It was certainly when I thought deadly medical conditions only happened to other people. Like I say, normal times.

So in the hospital I’m lying on my side, topless and facing the wall with my left arm crooked under my head. It’s how I was asked to lie here, but the position now feels oddly louche, as if I’m a life model and the portrait under construction is called Writer Is Quietly Relieved He Got the Novel Finished Because “Prolapse” Doesn’t Sound Like Something That’s Meant to Happen Inside Hearts. Two days earlier, I’d left the rehearsal room of the sitcom Back to go for a routine cast medical. A GP had put a stethoscope on my heart, pulled a face and referred me to the cardiologist.

It’s true to say I had sauntered into middle age while still treating my body like a skip

The heart doctor has a distinctive handshake, offered palm up with the fingers splayed. It looks like an apology and as soon as I sit down it becomes clear why he’s sorry. “I’m not saying you’re going to have a heart attack in the next fortnight,” he says slowly.

OK, well that’s… good.

“But if the problem isn’t addressed, then in the next two or four or six months… this heart will fail.”

There it is again, another word that warps the silence around it. “Fail”. As in: “epic heart fail”. It turns out that my heart has a prolapsed mitral valve. With every heartbeat, more than half the blood that should be pushed out of the left ventricle to do its thing around my body is flowing backwards into the left atrium. It means that the heart has had to work much harder than it should, growing and remodelling to keep the show on the road. This seems to have been going on for years. And now – time’s up.

“Unfortunately, valve repair isn’t something we can do with pills,” he says and I feel like I’ve gone very still. He puts it rather more gently than this but I gather there’ll be none of this newfangled noninvasive keyhole nonsense either. That’s for people who need to avoid a big old slash in the chest and their breastbone getting sawn in half and clamped open for hours. The snowflakes. No, it seems that if like me you’re a 47-year-old cardiac surgery virgin then there’s really no excuse not to do this the old-fashioned way: the method that maximises the chances of a good outcome because the surgeon can – as it was explained to me by another doctor – “see what the hell he’s doing”. Right. That’ll be lifesaving open-heart surgery for me then. Fine. “It’s going to be interesting to see how I react to this,” I think as I make my way urgently to the pub.

Mitral valve failure arises from a birth defect, and I was glad this was not “my fault”. And if it had been, I would surely have been advised not to think in terms of blame, and after a show of reluctance I would have agreed. But it’s true to say that I had sauntered into middle age while still treating my body like a skip, and of all the people who might find a brush with mortality useful, I was higher up the list than you might think. Hijacked by addiction at some point in the late 00s, my addled brain was on permanent lookout for the right “watershed”: no more cigarettes after this birthday, no more wine after this breakfast etc. Well, I’d got my watershed all right. You can’t operate on a beating heart – they were literally about to turn me off and on again. Watershed that, ducky.

Facebook Twitter Pinterest Robert Webb, right, and David Mitchell in Peep Show, 2015. Photograph: Channel 4

My mood during the weeks before the operation was the kind of hysterical calm you’d expect from someone who’s just made an appointment to get hit by a lorry. I wandered quietly around the house downloading audiobooks and trying not to have a heart attack. There wasn’t much work to do because I’d already finished editing Come Again, a novel I couldn’t help notice featured a fortysomething male who has just died from an illness that had been lurking unseen for years. His widow, Kate, finds herself back in 1992 and meets him when he’s still an annoying young man. She thinks she’s there to warn him. I like the idea my imagination had been trying to tell me something about my dodgy ticker. Thanks, imagination. Try something less subtle next time, would you? The story follows our heroine as she tries to do what many of us are attempting right now – she has to reconcile the lost past with the new present. In other words, she’s in mourning.

I remember talking to the friendly anaesthetist and the gurgling sound quite close to my ear as he pushed the anaesthetic through the cannula in my neck. Then time travel. Then my wife, Abbie, handing me a cup with a straw and history’s greatest ever sip of cold water. And I remember the relief that comes from knowing that it’s done. Ahead of me: six nights in hospital, three weeks before I could lift a kettle, four months before I was fit for work, a year of beta blockers to give my heart time to heal… but it was done.

There’s a long, thin vertical scar on my chest which bulges at each end, like the spaceship in 2001: A Space Odyssey

The first months of recovery felt like a light preview of old age, and I spent the winter minding my step. The dog-walkers smiled at me. Maybe they could tell I was now scared of dogs. Dogs, icy pavements and unpredictable toddlers – before coronavirus I was already giving everyone plenty of room. A daily walk, working from home and avoiding pubs – I’ve been doing all this since October. What else? Trying to be nicer on social media, limiting my contact with the news, turning inwards. To be fair, it’s possible that I’m confusing “grappling with the fragility of life and the ordinariness of death” with “being sober”. Either way, the world feels new.

Mainly I’m overtaken by gratitude. I was insanely lucky to get this over with before the virus struck, and my mended heart goes out to all those left waiting for treatment. I’m grateful for the Back medical and to all the doctors and nurses, the ones we applaud on our doorstep every week and perhaps always should have. I wrote a book about someone getting a second chance and I thought at the time it was a work of fiction. I feel re-blessed by my children. I thank what higher will brought me to a wife like Abbie.

There’s a thin, seven-inch vertical scar in the middle of my chest which slightly bulges at each end, like the spaceship in 2001: A Space Odyssey. Just below are three dots which mark where three tubes came out of my abdomen. The dots look like an ellipsis and remind me that you never know what’s around the corner…

Like most privileges, good health prefers to go unnoticed. The scars are beginning to fade and my life would be returning to normal by now if the times allowed. Assuming I’m spared by the plague and get the chance, one day there will be another room and another word that stops the show: “tumour” or “metastasised” or “sheer weight of that piano”. And it will be frightening, of course, but not mysterious. It will be a day like today.

For a while back there, the cliche was safe in my hands. I really did stop to smell the blossom in the trees; I listened to the songs of birds and admired the daffodils in all their trembling grace. No one can be permanently enthralled, but I won’t forget the moment when life got too close.

Come Again is published by Canongate (£16.99)