Scenario: This electrocardiographic (ECG) strip was recorded for a 3-day-old male newborn after an uncomplicated pregnancy and delivery. Cardiac monitoring was initiated because of a transient episode of cyanosis in which a follow-up ECG showed no signs of congenital heart anomaly. The newborn was deemed otherwise healthy, however there is a well-documented family history of cardiomyopathy. A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses electrocardiogram (ECG) interpretation for clinical practice. To send an eLetter or to contribute to an online discussion about this article, visit www.ajcconline.org and click “Respond to This Article” on either the full-text or PDF view of the article. We welcome letters regarding this feature.