To the Editor: Sick sinus syndrome (SSS) is characterized by dysfunction of the sinoatrial (SA) node that is often secondary to degeneration of the SA node and surrounding atrial myocardium. This could result in profound sinus bradycardia, sinus pauses, sinus arrest, SA nodal exit block, and inappropriate responses to physiological demands during exercise or stress. SSS can also be accompanied by AV nodal conduction disturbances and by paroxysmal supraventricular tachycardia as part of the tachycardia–bradycardia syndrome. Patients may present with symptoms of fatigue, lightheadedness, presyncope, syncope, dyspnea on exertion, angina, and/or palpitations. Drugs that depress sinus node function, including drugs that increase cholinergic tone, have been associated with SSS.