Purpose: There have been 3 published reports (4 cases) of symptomatic sinus bradycardia occurring after intravenous (IV) administration of the selective 5-hydroxytryptamine 3 (5-HT 3 ) receptor antagonist ondansetron. We report a fifth case in which the patient developed asystole after rechallenge with ondansetron. Summary: A 36-year-old pregnant patient with no cardiac history, status post cerclage for cervical insufficiency, experienced nausea in the post ambulatory care unit after administration of morphine and indomethacin for pain. After IV administration of ondansetron, the patient's heart rate decreased to the 40s and improved spontaneously. The patient experienced a second episode of nausea, another dose of ondansetron was administered, and the patient went into asystole. Advanced cardiac life support measures were initiated and chest compressions were conducted for 3 minutes with return of spontaneous circulation. The patient was monitored overnight with no development of new cardiac arrhythmias and was discharged from the hospital in stable condition. Conclusions: Sinus bradycardia after IV administration of ondansetron was observed in a 36-year-old pregnant patient status post cerclage. On rechallenge, the patient went into asystole. This case report adds to the available literature regarding ondansetron-induced cardiac arrhythmias and the possibility of asystole upon rechallenge.

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