• A 22-old man with recurrent palpitations. Ambulatory cardiac monitoring was obtained. • Atrial/supraventricular tachycardia was detected on the monitor. The patient was treated with antiarrhythmic drug therapy. • When cardiac monitoring data were reviewed by HRDx, sinus rhythm with artifact recording, rather than atrial arrhythmia was diagnosed. The patient was reassured, and drug therapy was discontinued.