Severe reactions to mesalamine products are rarely seen in pediatric patients. We report a case of a 12-year-old boy who had a severe cardiac reaction to a mesalamine product Asacol. Past medical history is significant for ulcerative colitis (UC) diagnosed at 9 years of age. Colo- noscopy one week prior to admission revealed pancoli- tis. He was treated with Asacol 800 mg three times per day and prednisone 20 mg/d. He was subsequently ad- mitted to the hospital for an exacerbation of his UC and started on intravenous solumedrol. He had improvement of his abdominal pain and diarrhea. The patient com- plained of new onset of chest pain upon initiating Asacol therapy. Electrocardiogram (ECG) revealed non-specific ST-T wave changes with T-wave inversion in the lateral leads. Echocardiogram (ECHO) revealed low-normal to mildly depressed left ventricular systolic function. The left main coronary artery and left anterior descending artery were mildly prominent measuring 5 mm and 4.7 mm, respectively. His chest pain completely resolved within 24-36 h of discontinuing Asacol. A repeat echo- cardiogram performed two days later revealed normal left ventricular function with normal coronary arteries (< 3.5 mm). Onset of chest pain after Asacol and im- mediate improvement of chest pain, as well as improve- ment of echocardiogram and ECG findings after discon- tinuing Asacol suggests that our patient suffered from a rare drug-hypersensitivity reaction to Asacol. Severe reactions to mesalamine products are rarely seen in pediatric patients. We report a case of a 12-year-old boy who had a severe cardiac reaction to a mesalamine product Asacol. Past medical history is significant for ulcerative colitis (UC) diagnosed at 9 years of age. Colo- noscopy one week prior to access revealed pancoli- tis. He was treated with Asacol 800 mg three times per day and prednisone 20 mg / d. He was subsequently ad-mitted to the hospital for an exacerbation of his UC and started on intravenous solumedrol. He had improvement of his abdominal pain and diarrhea. The patient com- plained of new onset of chest pain upon initiating Asacol therapy. Electrocardiogram (ECG) revealed non-specific ST-T wave changes with T-wave inversion in the lateral leads. The left main coronary artery and left anterior descending artery were mildly prominent measuring 5 mm and 4.7 mm, respe (ECHO) revealed low-normal to mildly depressed left ventricular systolic function. A repeat echo-cardiogram performed two days later revealed normal left ventricular function with normal coronary arteries (<3.5 mm). Onset of chest pain after Asacol and im-mediate improvement of chest pain, as well as improve- ment of echocardiogram and ECG findings after discon tinning Asacol suggests that our patient suffered from a rare drug-hypersensitivity reaction to Asacol.