If you want to be an excellent swimmer, you’ll really need to work on your . lungs
fingers
shoulders
heart

THIS IS IN FITNESS!

Lungs probably because I swim and you don't really use your fingers, but lungs is the best answer because you need to work on your technique instead of breathing a lot.

jomady. when the body perspires due to the temperature rising, trepidation, exercise, or a disease known as hyperhidrosis, then you would lose the sodium and potassium stored in your body, also known as the na+/k+-atpase enzyme.

a progressive heart disease that affects pumping action of the heart muscles.