Your Heart Underwater

Craig Bender   Jan 07, 2020

Scuba diving exposes your heart to a host of stressors related to immersion, cold, physical exertion,
emotional agitation, and more. Being familiar with what happens to your heart underwater is the first step
in preventing a cardiac event while diving.
Immersion: Just becoming immersed in water has an effect on
how your heart pumps blood. Immersion redirects blood from
the vessels in your legs to those in your chest cavity, which
means your heart has to enlarge to accommodate the extra
blood and pump harder to increase its output.
Cold: Water has high thermal conductivity, meaning you lose
more heat in water than in dry air of the same temperature.
When your body loses heat, your peripheral blood vessels and
small arteries constrict, which sends more blood to your heart
and increases resistance to blood flowing through the
periphery of your body. All of this raises your blood pressure,
so your heart has to exert itself more to maintain adequate
blood flow throughout the whole body.
Physical Exertion: Diving can be very physically demanding, and the addition of scuba equipment increases
drag and thus energy cost. Still, most dives at neutral buoyancy with no current require only short intervals
of slow?paced intermittent swimming, and you can always choose a low?intensity dive profile. Nevertheless,
all divers must be capable of dealing with unexpected events that require additional exertion.
Emotional Stress: Many divers are attracted to scuba diving because of the adventures it promises, but
sometimes these adventures come with surprises — perhaps even dangers. When you perceive a dive to be
particularly stressful, your autonomic nervous system activates the “fight?or?flight” response that increases
your heart rate, decreases your heart rate variability, and increases your risk of a cardiac event.
Most of the effects of diving on your heart fall within your body’s capacity to adapt, but cardiac events
remain the third leading cause of death in divers. If you remember just one fact, however, it should be that
60 percent of divers who died due to heart problems experienced warning signs prior to diving. So be
aware. Dive smarter. Dive safer.
For more info, visit DAN.org/Health.
Take a quiz at DAN.org/Quiz to test your knowledge of cardiovascular risk factors for diving