Is Elevated Heart Rate Normal Post Treatment For Pneumonia?

I am off Cardiazem now, after being hospitalized for pneumonia and consequent atrial fibrillation. My heartbeat was going down to 45 with the medication post hospitalization. Right now my heartbeat is 91 ( I climbed a flight of 14 stairs.) is that okay? I thought of taking a Cardiazem pill but am not sure it can be used sporadically this way?