I had just seen the cardiologist and had an echo cardiogram and my heart function was normal (I had myocarditis and temporary heart failure a year ago but recovered and am being monitored) and I am on a beta blocker (a certain kind that allegedly does not make asthma worse) for high blood pressure. My asthma/possible infection was getting worse (sob more mucus) so I took the doxy which I have on hand for this (given by the pulmo) and the prednisone (from the allergist and the pulmo). Whenever I am ill even on a beta blocker my HR rises about 15 points above what it is normally and I can tell. (90s instead of mid 70s during the day) That is very consistent. As the pills work in a few days my HR goes slowly down and back to normal where it is right now. I finished the doxy today and lowered the pred to 20 mg for a few days then will drop it again. Fingers crossed! I am not 100% back to normal - I'm tired - but my HR is and that bodes well. Maybe you need some blood work to show infection? Since the days of fitbit and other heart rate monitors it is becoming more and more known that illness will raise your heart rate significantly. As the cardio about that if you have a chance. The heart pumps more to move around the fighter cells or whatever to take on the infection or something like that!