However, clinicians must be aware of and alert for more serious underly-ing conditions. In this article, we report the case of a young man who presented with palpitations and a wide complex tachycardia on electrocardiogram (ECG). The patient’s symptoms were caused by atrial fibrillation with a rapid ventricular response due to underlying Wolff-Parkinson-White (WPW) syndrome. WPW syndrome, which is classified among the par- oxysmal supraventricular tachycardias (PSVTs), is a relatively uncommon cardiac conduction disorder that occasionally may cause early excitation (preexcitation) of the ventricles due to antegrade atrioventricular (AV) conduction through an accessory pathway. Patients with WPW syndrome may present with preexcited atrial fibrillation. ECG tracings of patients who have WPW syndrome typically reveal a narrow QRS com-plex, but WPW syndrome associated with preexcited atrial fibrillation may produce a wide QRS complex on ECG. These ECG findings are commonly confused with other causes of wide QRS complex tachycardia, such as ventricular tachycardia.