Chaotic atrial mechanism (CAM) is a serious arrhythmia occurring in elderly patients with advanced heart disease, and appears to be related to multifocal atrial activity. The properties of CAM suggest it is an automatic ectopic rhythm, and may be produced under different combinations of conditions. CAM may progress to atrial fibrillation, just as ventricular tachycardia may lead to ventricular fibrillation. Drug-enhanced automaticity, distension of atrial walls, ischemic heart disease, or space-occupying lesions accounted for our cases. These appear to be similar to the currently accepted responsible events for pathologic ventricular automaticity. Both CAM and the ectopic automatic ventricular rhythms are associated with a high mortality, since both occur in patients with advanced heart disease.The additive antiarrhythmic action of combined propranolol and quinidine therapy may be helpful in managing CAM.