Masturbating daily long sessions, fast heart beat, warm chest, both lasting for long periods, BPM ranging from 60 to 90. Heart problems? Should I stop masturbating, to allow for body to rest? I'm 19

You're a man! Hey buddy! You're 20 years old. I'm glad you're enjoying your body like all the other guys. This physiologic response is fine. I hope you get just as excited when romance comes into your life. If you're taking too much time focused on erotica, and it's compulsive, we can help. Otherwise, enjoy being young. Maybe you could even talk with Dad about your changing body.
Define long periods. Not sure how to answer this... Depending on how "long" these "sessions" last, maybe you should stop them so you can go about a normal life. Seriously, if you are saying you get heart symptoms with masterbating, perhaps you should consult a cardiologist first. Males your age should not have any symptomatic problems while "loping the mule". Get your heart checked out, but otherwise should be ok.