Verified answer

No, your heart does not slow down when under water. How long you can hold your breath is purely a matter of how fast your body creates carbon dioxide (CO2). This happens in the lungs as the heart pumps blood: CO2 is exchanged for oxygen (and the other gases that make up air). The more you work, the more the heart pumps and the more CO2 is released into your lungs. The urge to breathe is actually caused by your brain sensing the build up of CO2, not by the lack of air.

Above water or below, how long before the urge to breathe starts is the same, given the same activity.

yes it dose because if you hold your breath right now your heart beats slower so if your under water its the same. :)

yes, it does. your heart beats because it pumps oxygen to different parts of your body. the less oxygen your heart needs to pump the slower it pumps. and when you hyperventalate, your heart beat gets exceedingly faster.

your not breathing duh?? comon scence hello????