Six days after having a laproscopic appendectomy (appendix did not rupture but was absessed), I had severe stabbing pain in shoulder blade area, tightness in chest, and shortness of breath. Since my family has a history of blood clots I thought that I had a clot to the lung or was having a heart attack. My diagnosis in the ER was pericarditis. I am a 62 year old female with excellent health, take no meds, no heart conditions, and no health problems. After appendectomy, I was placed on Bactrim and Flagyl for 5 days. After taking meds for 4 days, the shoulder pain, tightness, and breathing issues began. I suspect that the pericarditis was not random but rather caused by appendicitis, the surgical procedure, or reaction to antibiotics. Trying to see if you have any guesses as to the most likely cause.