**"Nearly one-third of all diving fatalities are associated with an acute cardiac event."** Scuba diving is an appealing recreational activity for people of all ages. Indeed, diving in favorable conditions requires little exertion, making it easy for the uninitiated to assume that diving is a safe and effortless pastime. But it is essential to keep in mind that during any dive, perilous conditions and circumstances can arise that may call for vigorous exercise on a moment's notice. Immersion alone is a stressor on the body, especially the heart and circulatory system. People who have limited exercise capacity may be pushed to their limit by diving — to the point of serious injury and even death. This section explains some basic information about the heart in relation to diving to help keep you safe and healthy as you dive.