As a keen swimmer and golfer, 60-year-old Michael saw no reason to worry about his heart. So when an annual health check showed his right coronary artery was dangerously blocked, he was taken aback.
"I had an angiogram on a Monday. The surgeon came over straight away and told me they'd found a 99% blockage, and would be operating on my heart that Thursday," he says. "It came as a shock as I'm pretty healthy, and I'd had no symptoms – no chest pain or anything like that. I felt absolutely fine."
In fact, Michael did have a warning sign for heart disease: he had been having problems getting an erection.
"I've been taking sildenafil [the generic name for Viagra] for a couple of years. I just thought it was part of getting older, but was surprised when my cardiologist told me it can actually be a symptom of blocked arteries. I was exceedingly lucky to have it picked up in time. I could have been a corpse on the golf course."
Half of all men between the ages of 40 and 70 will experience erectile dysfunction. While the problem doesn't cause heart disease, the two often occur together – study after study has shown that men with ED are dramatically more likely to develop heart disease and have a heart attack or stroke. One German study from 2010 found men with erectile dysfunction are twice as likely to die within the next two years as those without, prompting some experts to call the phenomenon "the canary in the trousers".
If a man's arteries become blocked with cholesterol – as a result of genetics, and/or lifestyle factors such as smoking, a poor diet and lack of exercise – it will affect the vessels all over his body. The arteries supplying the penis are relatively small, just 1-2mm wide, and so they become blocked more quickly than others. The blood flow to the area is reduced, meaning erections become more difficult.
But if the blood flow is weak here, it is highly likely that it is also weak in arteries supplying the heart, raising the risk of a heart attack. In fact, some studies suggest that women with heart disease may also suffer sexual dysfunction: the clitoris, like the penis, is a vascular organ, and also relies on healthy blood flow for successful orgasms.
The trouble is, most people don't know that sexual dysfunction can be a warning sign of something more serious. Dr Graham Jackson, a cardiologist and the chairman of the Sexual Advice Association, would like to change that. "People aren't aware of the underlying causes of their problems because they feel well otherwise," he says. "They'll say, 'It's my age' or 'I'm nervous because I'm in a new relationship.' But every man with erectile dysfunction should have their heart and blood pressure checked."
Since 60% of heart attacks happen with no warning, taking action when ED starts could save lives. And this is not just a problem for older men – Jackson has seen men in their 30s and even 20s suffering erectile dysfunction because of clogged arteries.
Heart disease isn't the only risk. ED is also a predictor of stroke, because when the arteries are narrowed there is more chance of a blood clot, which can spread to the brain. It is also a common complication of diabetes. But embarrassment stops people seeking help, says Jackson. "We need to encourage men to talk to their spouses about this problem, instead of making an excuse to avoid sex.
"One couple came to see me, and when I asked the man how long he'd had erectile dysfunction, he told me it had been happening for five years. His wife looked at him and said: 'But this is the first I've heard of this.'" He adds that Viagra-type drugs can mask the problem, and many men still buy them online to avoid talking to their doctor about their difficulties in the bedroom. As a result, their risk of heart attack is never picked up.
However, many doctors are unaware of the dangers, too. Indeed, when Michael first went to his GP there was no discussion of the possible underlying causes, and instead the doctor simply prescribed a Viagra-like drug. "There are so many adverts for Viagra and my spam basket is half full of emails about it," says Michael.
"It feels like a large proportion of men my age are probably taking it, with no idea that their heart could be in trouble. The medical profession needs to pay more attention and do more testing."
The good news is that if heart disease is picked up in time, it can be successfully treated with lifestyle changes, medication or surgery. Jackson warns there is no hard evidence that "fixing the heart will fix the sex", although some studies have shown that taking a statin (which lowers cholesterol) can improve erections.
Three days after Michael was found to have a dangerously blocked coronary artery, surgeons inserted a stent to prop the artery open. Now he is keen to get more men going to their doctor to be checked up. "When it comes to sex, people keep things to themselves. But this is an easy way to catch heart problems at an early stage and treat them before the worst happens."
Michael's name has been changed.
• 14 February is the Sexual Advice Association's Thinking About Sex day, sda.uk.net.