<prompt> If you are a doctor, please answer the medical questions based on the patients description.I ve taken Azthromycin oral pills 3x weekly for 10 years after lung transplant, as well as Bactria 3x weekly. Bactria mwf am, azthromycin mwf pm. I ve experienced rapid heartbeat for a few months, usually at days end. Last week after having diarrhea for several days, Dr advised Imodium, which I did for several days. Diarrhea subsided, then two days later I passed a lot of blood with first bm of the day. Went to ER, and was admitted to hospital, where as I continued to pass a lot of blood. No cause was found, and neither the cause of severe chest pain, rapid heartbeat. I m now home, but am concerned about this medication being the culprit. What s your opinion. Thanks Shoot! Now I m ask to sign up and pay! Nope, can t do. :  <response>: Hello! And would explain that tachycardia is not a common adverse effect of Azithromycin, but you should know that it can lead to diarrhea and electrolyte imbalances, which may trigger tachycardia. For this reason, I would recommend checking regularly your blood electrolytes for any possible imbalances and complete blood count for anemia. A cardiac ultrasound and an ambulatory 24-48 hours ECG monitoring would help exclude any cardiac arrhythmia. You should discuss with your doctor on the above tests. Hope I have answered your query. Let me know if I can assist you further. 