We recently described a syndrome characterized by an ECG pattern of right bundle branch block and persistent ST segment elevation in leads V1 to V3 in patients suffering from aborted sudden cardiac death and not having demonstrable structural heart disease. We present new observations on this syndrome, especially those related to asymptomatic and intermittent forms. Forty-seven patients with the described ECG pattern were identified; 32 were symptomatic with syncope and sudden death aborted by cardiopulmonary resuscitation. Eleven patients received pharmacologic therapy, mainly amiodarone and/or beta-blocking agents, and 21 patients received an implantable defibrillator with or without pharmacologic therapy. Three of the 11 patients on pharmacologic therapy died suddenly during follow-up, while 9 of 21 patients with an implantable defibrillator used the device during follow-up. The remaining 15 patients were asymptomatic when first seen. Three patients died suddenly after 6 years, 3 months, and 2 months of follow-up without treatment. Another patient received an implantable defibrillator after syncope and had subsequent episodes of ventricular fibrillation terminated by the defibrillator. The other 11 patients remain asymptomatic without (6) or with (5) treatment with beta blockers. In 14 of the 47 patients, the ECG normalized momentarily during follow-up but later became abnormal again. During transient normalization of the ECG, administration of ajmaline or procainamide unmasked the described ECG pattern in six patients who received the drug. Long-term follow-up of survivors failed to show progression to any form of right or left ventricular cardiomyopathy.