A healthy woman in her 20s presented to the emergency department with palpitations after completing a run. On presentation, her blood pressure was 125/80 mm Hg, heart rate was approximately 200 beats per minute (bpm), and oxygen saturation was normal on room air. Cardiac examination was notable for a normal jugular venous pressure with absence of a prominent A wave, a tachycardic and irregular rhythm, normal apical impulse, normal heart sounds, and no murmurs, rubs, or gallops. Physical examination results were otherwise unremarkable.