The static breathhold competitions are supported by Suunto heart rate monitors.

Notes on heart rate: training cardio at a level of 75-80% of your maximum heartrate (220 - half your age) will increase your oxygen uptake (fitness) and will lower your resting heart rate. During breathholding your slowing heart rate will give you an indication of when your Diverespons has been established (reducing your use of oxygen), normally a heart rate half of your starting heart rate. The drop in heart rate is called bradycardia.