When You Have a Heart Condition, Diagnosed or Not
The cold shock response is not a metaphor. Within the first 30 seconds of cold water immersion, your body triggers a gasp reflex, spikes heart rate, and constricts peripheral blood vessels sharply. For a healthy person this is uncomfortable. For someone with an undiagnosed arrhythmia, a narrowed coronary artery, or hypertension, it can trigger cardiac arrest before they reach the far end of a plunge pool.
