I had a resting heart rate of 106 while I was taking 120 mgs of clen at the end of my last cut cycle. Blood pressure was good though. I did cardio and the fitness test on the stair climber always said I was in poor condition because my Heart rate was rockin. there are some support supps you need to take with the clen that will help protect your heart from damage. Do a search I think you will find more info than you want