People who have had a recent cardiac arrest may worry about triggering another episode, with too much physical exertion. 
And they might even wonder whether an activity like sex might be dangerous. But a new study presented at a meeting of the American Heart Association draws a reassuring conclusion. 

How often does sex trigger a cardiac arrest?  The short answer is very rarely. Researchers from the Cedars-Sinai Heart Institute in Los Angeles examined the medical records of 4,557 cases of documented cardiac arrest in a community in the northwestern United States. The heart stoppages occurred between 2002 and 2015. Of those cases, just 34 cardiac arrests occurred within one hour of sexual intercourse. 

For men and women combined, sexual activity was a potential risk factor in just 0.75 per cent of all episodes of cardiac arrest. If you're wondering, those who had a cardiac arrest immediately following sex had the same amount of pre-existing heart disease as those who weren't having sex when their heart stopped.

Men had a higher risk than women. Of the cardiac arrests that happened within an hour of intercourse, 94 per cent occurred in men. Another way of looking at it is that for men, one out of every 100 cases of cardiac arrest occurred following sex; for women, it's one out of every 1000 cases of cardiac arrest. Still, even for men, the numbers are small enough to conclude that worrying that your heart will stop is no reason to stop having sex after a heart attack. 

The bigger issue, say the authors, is what happens immediately after your heart stops. It's critical that bystanders begin CPR irrespective of the circumstances. Clearly, sudden cardiac arrest during sexual activity is almost always witnessed by the partner. But in this study, CPR was performed in only a third of the cases. That led the researchers to conclude that the sexual partners need some education and maybe some special training. 

We've been talking about cardiac arrest. What about the risk of sex triggering a heart attack? Some people think (incorrectly) that a heart attack is the same as a cardiac arrest, but it isn't. A cardiac arrest is a heart stoppage most commonly caused by ventricular fibrillation. A heart attack (doctors call that an acute coronary syndrome or ACS) refers to damage and death to heart muscle.  ACS is triggered by a sudden blockage of one of the coronary arteries that bring fresh blood and oxygen to the heart muscle. 

Studies show that sex can trigger heart attack. But it doesn't happen very often.  A study published in JAMA found that sexual activity triples the risk of a heart attack. Sounds scary, but it isn't if you understand statistics. For a 50-year old who just had a heart attack and isn't in shape, the risk of exercise is 10 heart attacks per million patients per hour of exercise. Having sex boosts that risk to 30 heart attacks per million patients per hour of sex. That's not a big absolute risk.

If you want to lower the risk even more, get back into shape. The risk of heart attack for a 50-year old man who exercises regularly is one heart attack per million people per hour of exercise.Having sex triples the risk to a grand total of three heart attacks per million people per hour of sex.  

How much exercise can you get having sex? As a form of working out, it's ironic that sex leaves a lot to be desired. Doctors measure the impact of exertion with something called metabolic equivalents or MEs. One ME is the amount of oxygen consumed while sitting at rest and is equal to 3.5 ml O2 per kg body weight times the number of minutes of activity. Sex averages two to three MEs, and sometimes rises to three to four MEs at orgasm. Light housework averages two MEs, climbing stairs scores three to four MEs, and shoveling light snow reaches six to seven MEs

For the person at risk of a heart attack, having sex on top means your risk could be as high as a little over five MEs, lower than two to three MEs expended when you're on the bottom. There is also a slightly increased risk when having sex with a new partner in an unfamiliar place.

You can read a good backgrounder here.

If sex isn't all that risky, you might be wondering what else should give heart patients pause for concern. Well, put money troubles at the top of the list.  Researchers in South Africa studied 106 patients who admitted to hospital with a heart attack. They found that patients in severe financial difficulty were 13 times more likely to have a heart attack than those who had less trouble making ends meet.   

That makes stress as likely as cigarette smoking and high blood pressure to trigger a heart attack. The researchers also found that patients who were depressed had three times the risk of having a heart attack compared to those who said they were happy. 

The people who do cardiac rehabilitation programs say they teach patients how to manage stress. But that's after they've had a heart attack. Researchers say doctors need to ask their patients if they are under financial and other forms of stress before it happens. More research is needed. Until then, more sex and less financial trouble seems like a sensible prescription.