Harvard Heart Letter

Ask the doctor: Is swimming in cold water okay for my heart?

Q. I spend part of every summer on the coast of Maine. One of the things I love to do there is swim in the ocean for 20 or 30 minutes. The water is cold (55 F) but I don't mind. I'm almost 80. I had my mitral valve repaired five years ago, and my heart rate is sometimes irregular. Are my cold-water swims okay for my heart?

A. Swimming is an excellent exercise for the heart, arteries, lungs, and muscles. If you enjoy swimming in cold water and have been doing it for some time with no ill effects, it's probably fine for you. But your question worries me for a couple of reasons.

The human body is adapted for life on dry land and the downward tug of gravity. Immersing the body in water squeezes blood from the extremities into the chest. This makes the heart work harder and increases blood pressure. Holding your breath and putting your face in the water makes the heart slow down and also elevates blood pressure. This diving response, commonly called diving bradycardia (bradycardia means slow heart rate), is a well-studied phenomenon. It doesn't necessarily require depth — bradycardia and a spike in blood pressure can occur when the face is immersed in water even at the surface, as happens during swimming.

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