Between September, 1971, and April, 1982, 11 patients (seven female) with left atrial myxomas underwent surgical resection at Cedars-Sinai Medical Center. The tumors ranged in size from 4 to 9 cm (mean 6.3 cm) and were attached to the interatrial septum (four superiorly, four inferiorly), the free atrial wall (one posteriorly, one at the dome), or both (one). Although all patients were symptomatic preoperatively, arrhythmias were uncommon; only one had chronic atrial fibrillation, and two others had had single episodes of paroxysmal atrial fibrillation in the immediate preoperative period. Early postoperatively, all but one patient had episodes of atrial fibrillation (eight patients), atrial flutter (four patients), junctional rhythm (six patients), sinus arrest (two patients), or complete heart block (three patients). Ten patients required antiarrhythmic therapy, and two required permanent pacemaker implantation. After a mean follow-up of 48 months (range 7 to 124), seven patients continue to have episodic or chronic supraventricular arrhythmias, with only three patients not using antiarrhythmic drugs regularly. The pathophysiological basis for these arrhythmias is unclear, but some patients appear to have sustained injury to the sinus node or atrioventricular node, while others have developed interatrial or intra-atrial conduction delays. Attention should be directed to the basis of these arrhythmias and conduction disturbances, as surgical technique may be the major determinant of this early and late postoperative complication.