Researchers from St Thomas's Hospital in London found couples in long-term relationships were far less likely to have heart attacks while having sex than those having affairs or one-night stands, BBC reported. Sex with someone who is not your spouse increases your risk of having a heart attack according to them. The risk of extra-marital sex increases even more when there is a significant difference in age between the partners, Cardiologist Graham Jackson said at a sexual health conference in Hamburg, Germany. He told the conference: "We found that 75% of the cases of sudden death during sexual activity involved people who were taking part in extra-marital sexual intercourse." But he added: "Only 1% of all heart attacks are triggered by sexual activity." In general, sex puts the same amount of pressure on the heart as a brisk 20 minute walk, with an orgasm putting the same strain on the heart as walking up a flight of stairs.