I have this unknown lower abdominal pain since July, 2014. I have sought medical helps from OBG, Urologist and Gastroenterogist and went through cervical, bladder, cystoscopy ultrasound and results all went back negative. GI doctor prescribed me Nortriptyline 10mg and it helped ease the pain and helped me sleep. As advised, I should only take it when I feel the pain and I did so. Lately I started having noticeable heart pounding fast and irregular and I wonder if this was the side effect of Nortriptyline. Can one take this medecine as long as one needs? Is the side effect a concern? It certainly made me concerned with the heart palpitation.