Surgeons like to say that when someone suffers a heart attack, time is muscle. The heart depends on a continuous supply of oxygen from the coronary arteries; if these become blocked and that supply stops, the heart’s muscle cells start to die off within just a few minutes. In many cases, unless surgeons can relieve the blockage within the hour, more than 1 billion muscle cells are irreversibly lost.

Those who survive are often left with permanent heart failure – a group which includes approximately 450,000 people in the UK. Within the five years following an attack, 50% of them will no longer be alive. “Eventually their hearts become so weak that they can’t sustain sufficient blood flow and they just stop altogether,” says Sanjay Sinha, a cardiologist at Addenbrooke’s Hospital, Cambridge.

But even within the next five years, regenerative medicine may provide a radical new alternative: growing live, beating ‘heart patches’.

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The challenge is that unlike some of our other organs, like the skin and liver, the heart has a very limited ability to self-heal. Heart muscle cells replicate at a rate of just 0.5% a year, not sufficient to repair any significant damage. Instead, the dead cells are replaced by thick layers of tough, rigid scar tissue, meaning that sections of the heart simply cease to function.