Hi, Im An 18 Year Old Girl. I Weigh About

Hi, im an 18 year old girl. I weigh about 130 pounds and im 5'8. Ive had arthritis all my life and was taken out of PE and all sports at a very young age. Although I eat well and exercise i decided i needed to work on my cardio because i have zero endurence. When I go to the gym my heart rate is at 140-170 and never drops below these very high levels, im worried and want an opinion on how to help myself become healthy and if its dangerous to be working out with this high of a heartrate