S₄ gallop in a neonate following a prolonged period of supraventricular tachycardia

Phonocardiogram recorded at the apex in 17-day-old neonate with severe left ventricular dysfunction secondary to a prolonged episode of supraventricular tachycardia. The electrocardiogram demonstrates Wolff-Parkinson-White syndrome with a prominent delta wave. In the recording, a S₄ is heard coincident with the P wave on the electrocardiogram during the period of atrial contraction.