This is the electrocardiogram of a 3-month old infant with a large ventricular septal defect. It demonstrates left atrial enlargement and biventricular hypertrophy.

Characteristic features include sinus tachycardia at 160 beats per minute. Left atrial enlargement reflected by the broad, notched P waves in leads I, II, aVF, V4, V6 and V7. And the wide, negative terminal portion of the P wave in V1. Right ventricular hypertrophy is reflected by the tall, dominant R waves in leads V3R and V1. Left ventricular hypertrophy is reflected by the by the tall, dominant R waves in lead V6. Biventricular hypertrophy also is reflected by the large biphasic complexes in mid precordial leads V2 and V4. This feature is called the Katz-Wachtel phenomenon.