Coronary sinus (CS) diverticula have been reported to be the anatomic basis of some posteroseptal accessory atrioventricular pathways. During 1 year, 53 patients with Wolff-Parkinson-White syndrome referred to our center for catheter ablation were found to have posteroseptal or left posterior accessory pathways. The accessory pathway was associated with an anomaly of the CS in seven patients (13%), including six diverticula of the CS or its branches and one aneurysmal CS. Four of the CS diverticula were visualized by transesophageal echocardiography. Diverticular appear as echolucent, contractile pouches on the epicardial surface of the posteroseptal or posterior left ventricle that connect to the CS by an isthmus. Previous reports have suggested that accessory pathways associated with CS aneurysms have rapid conduction times and may be associated with an increased risk of rapid ventricular response during atrial fibrillation and sudden death; five of our seven patients had a short preexcited R-R interval in the range of 172 to 225 msec during atrial fibrillation. In summary, many, if not the majority, of CS diverticula associated with preexcitation can be visualized by transesophageal echocardiography.