Cold exposure can potentially cause heart attacks in certain individuals. The cold-shock response activates the sympathetic (“fight or flight”) nervous system, which increases the heart rate and blood pressure. Although this response is important for preserving core body temperature in the cold and is well tolerated by individuals without apparent health conditions, the sudden increase in stress on the heart could potentially cause a heart attack in people who may be vulnerable.[1][2]
Vulnerable individuals also may be at an increased risk for sudden cardiac death when the face is submerged during cold water immersion. Although cold water immersion typically involves immersion up to the chest or neck, which triggers the cold shock response and activates the sympathetic nervous system, full-body submersion, in which the face is under water, also triggers the “diving response,” which slows heart rate through a parasympathetic (“rest and digest”) nervous system response. The conflicting signals coming from the two limbs of the autonomic nervous system to the heart have been proposed to cause an “autonomic conflict”, which could potentially cause sudden cardiac death in vulnerable individuals.[3] Although this has yet to be proven, cold water submersion is known to increase the incidence of cardiac arrhythmias in individuals without known health conditions,[4][5][6] and it has been proposed that sudden cardiac death may at times be the actual cause of deaths from cold water submersion that were previously attributed to drowning or hypothermia.[3]