Johnny Cash and June Carter met backstage at the Grand Ole Opry. It was a little like a country song: he was married, she recently divorced, and an affair ensued; both singers had young children, and Cash would have three more with his first wife before she left him in 1966, citing his drinking and carousing. Two years later, he proposed to Carter on stage and, despite having turned him down numerous times before, she accepted. They'd each found a life match.

It ended like a country song, too. In 2003, Carter died in Nashville of complications from heart surgery, and Cash followed her to the grave four months later. The heart complication for him, it seemed, was that it was broken: “It hurts so bad,” he told the audience at the last concert he would give. The pain, he said, tuning his guitar, close to tears, was “the big one. It's the biggest.”

Cash was speaking for many a bereaved partner – and well before Johnny ever met June, scientists had noticed that cases of spouses dying in rapid succession were not at all unusual. By the 1980s, medical researchers had started writing about “stress cardiomyopathy”, or “apical ballooning syndrome”, the ungainly name for the peculiar condition whereby an individual's brain, following an intense emotional trauma, would inexplicably release chemicals into the bloodstream that weakened the heart – in some cases, causing it quite literally to break.