Forty-four patients with sick sinue syndrome (SSS) who had been treated with a permanent pacemaker were followed for an average period of 39 months. Fifteen patients had bradyarrhythmia alone (group 1) and 29 had bradycardia-tachycardia syndrome (group 2). Eight patients, all from group 2, died within a short period following pacemaker implantation. They all had ischemic heart disease, congestive heart failure and a short history of the symptomatic dysrhythmia. Eleven patients developed stable chronic atrial fibrillation, which terminated the clinical syndrome. In the remaining 25 patients, all without evidence of ischemic heart disease, the dysrhythmia persisted although symptoms were successfully controlled following pacemaker therapy. Based on these observations and data obtained from other surveys, we delineated three courses of SSS: 1) a subacute course, characterized by a short-term survival; 2) a transient, self-limited course in which conversion to stable atrial fibrillation occurs; and 3) a chronic course, in which the dysrhythmia persists and permanent pacemaker therapy is indicated.