When i take deep breath i feel prickle in my chest on left side only, and a dr said my heart beat low but nothing serious, whats wrong with my heart?

2 problems: The prickle in the chest most likely comes from chest wall-muscles-joints, very unlikely to be related to heart. For saying your heart beat is low, you need a 24 hour Holter monitoring.

Probably nothing.: For someone your age who is in good condition a heart rate in the 50-60s is normal. In your case I don't know how low low is. I assume you discussed the prickle in your chest with ur doc. However, since you are still asking questions you should see him/ her again so your specific questions can be fully answered. Good luck.