Vassilios Avlonitis sits in a cramped basement office in St Thomas’ hospital in London. He may be a distinguished cardiac surgeon, but in the cash-strapped NHS, he still has to share a tiny workspace. He is immaculately turned out, with a kind face and the sort of hands I imagine playing the piano. And it’s his hands that I can’t stop looking at. The same hands that picked up a radial saw and cut through my breastbone. The same hands – the only hands – that have literally touched my heart. The hands that stripped veins from my leg and used them to replumb my broken heart. I have this man to thank for saving my life. And the cash-strapped NHS, of course.

It is 50 years since Christiaan Barnard performed the first successful heart transplant operation. At the time, it was akin to putting a man on the moon. My operation was just a simple quadruple heart bypass, not a transplant. The day after the terrorist attack at Borough market, I had a heart attack. The team at St Thomas’ discovered that my heart was almost completely blocked up with gunk. And they fixed me. So now I am overly aware of all things heart-shaped – both the pointy red heart shape that gets tattooed on arms and printed on Valentine’s cards and the fist-sized muscly pump that propels blood around our bodies.

That there are two very different hearts is interesting. One is the heart of medical science. The other is the heart of countless poems and religious writings, the heart that is a symbol of our emotional life, indeed, for some, a symbol of our very existence. Barnard’s pioneering operation was an important stage in their long and complicated divorce because prior to this first heart transplant operation, it was the beating of our hearts that was widely regarded as signifying our being alive. Death was the cessation of the heartbeat because the heart was seen as the fountain of life. That is why the Japanese transplant surgeon Juro Wada, who performed a heart transplant in 1968, was charged with the intentional homicide of the donor. The logic was clear: if the heart was still OK, then the donor must still have been alive when the heart was removed.

In this country, the Daily Express led a campaign against heart transplants, stoking up fear that organs were being harvested from those who could have been saved. The questions kept on coming. If the heart was indeed the source of life, what did that mean for the identity of the recipient? And in apartheid South Africa, this anxiety was given a racial dimension – particularly after Barnard’s second operation, in which a mixed-race man’s heart was used to save a white man. The Guardian commented, with bitter sarcasm: “There is no provision under the Group Areas Act for black hearts to beat in white areas.”

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It was partly in response to some of these issues that we now we think of death as the shutting down of a part of our brain, with brain death becoming the accepted medical definition of death from the 70s onwards. Nevertheless, it was still extremely disconcerting to hear Mr Avlonitis tell me that, as a part of the operation, he had stopped my heart beating for the best part of an hour. Medical science may have shifted our existential centre of gravity from the heart to the brain, but for an old sentimentalist such as myself, the heart will always feel like the centre of my being.

It was a conversation with Rowan Williams, the former archbishop of Canterbury, that helped me understand why I still think that. Imagine how peculiar it would be if scientific advance created an artificial replacement pump for the heart that pushes blood around the body in one continuous flow, without a beat. This thought got us talking about Shakespeare and his use of iambic pentameter. “But, soft! What light through yon-der win-dow breaks?” The rhythm – ber-bum, ber-bum, ber-bum, ber-bum, ber-bum – is the rhythm of our heartbeat. That is what makes Shakespeare’s poetry so ingressive, so affecting. It picks up on the earliest noise we hear, in the womb. And this rhythm accompanies us throughout our lives. Rowan compared it to the tide coming in and out. It is a sort of anchor, a fixed and continuous reference on which we come to attach a sense of self. This is the beat that monks and mystics have listened out for in their periods of silent prayer, as if listening to this is to spend time deliberately conscious of the constituent conditions of being human. There would be something profoundly disorientating in having an artificial heart that didn’t need to beat out this constant and uninterrupted tempo.

We have strayed a long way from the calm and collected Mr Avlonitis, who smiled weakly at my tendency towards exotic metaphysical speculations. He is a scientist. And his subject is a pump. “Doesn’t that make him just a glorified plumber?” I tried to provoke him, for conversation’s sake. “Hasn’t the brain taken centre-stage now?” And with that my mind was off, thinking about how interesting it was that we have become a far more rationally oriented culture at around the same time that the brain has become the preeminent organ in the human body. But he was not provokable. No doubt it is the quality of imperturbability that makes him such an effective surgeon. If he was a plumber, he was a plumber that has saved my life. Not just that, but I feel better today than I have for a great many years. I would say that I am born again. And I thank him, and all the staff at St Thomas’, from the bottom of my heart.

Radio 4 will be marking 50 years since the first heart transplant with a range of programmes this week with Giles Fraser’s series This Old Heart of Mine, Monday to Friday at 1.45pm. Visit bbc.co.uk/radio4