A 58-year-old male patient, active smoker, had been previously assessed for paroxysmal palpitations, with the following baseline electrocardiogram (ECG) (Fig. 1). Structural heart disease had been excluded by echocardiography. He was admitted to the emergency room with these symptoms, and the ECG then showed irregular narrow complex tachycardia (Fig. 2). Although F waves were visible in the inferior leads, the patient was given 6 mg of intravenous adenosine by the emergency physicians to better determine the underlying tachycardia and make a differential diagnosis with other supraventricular tachycardias. Was this the correct approach?