By the way, doctor: Should I worry about this irregular heartbeat?
Q. At 86, I'm still competitively racing frostbite dinghies for about two hours once a week, but only in light winds. I've noticed that my usually regular heartbeat becomes irregular during the races and for hours afterward. It feels like a weak beat after every two normal heartbeats. Is this a normal exercise reaction?
A. It sounds like you might be having trigeminy (pronounced try-JEM-ah-nee), an abnormal rhythm in which you have a premature beat among every three heartbeats. If we could get an electrocardiogram (EKG) during these palpitations, we would probably see two normal beats and then an early abnormal one. The reason the early beat feels weak is that your left ventricle — the largest and strongest chamber of the heart, which pumps blood out of the heart into the rest of the body — hasn't had a chance to fill completely before it's forced to contract by the early electrical activity.
As long as you are not having symptoms such as fainting or near-fainting, I wouldn't worry too much about this irregular rhythm. On the other hand, if you do start to have such symptoms, you should get medical attention as soon as possible. The significance of these abnormal beats is also more troubling if you have known heart damage from a heart attack or other disease.