Background: Herbal medicines may have significant adverse effects which are not suspected or recognized. Case Report: A 34-year-old female developed severe nausea, vomiting, drowsiness, prolonged QT_c, and episodes of nonsustained ventricular tachycardia following self-administration of a herbal remedy, Passiflora incarnata L., at therapeutic doses. The possible association of symptoms with passiflora was not recognized for several days. She required hospital admission for cardiac monitoring and intravenous fluid therapy. Conclusions: Passiflora incarnata was associated with significant adverse effects in this patient. It is important to ask specifically about the use of herbal medicines in patients with undiagnosed illnesses.