A case of massive pulmonary arteriovenous fistula, diagnosed and treated in the first week of life is reported. A concept of severely altered intrauterine and neonatal pulmonary blood flow is proposed, with consequent left ventricular overload manifested electrocardiographically by left axis deviation and left ventricular preponderance. Consideration of this malformation in seriously ill cyanotic infantswith a radiographic density and these electrocardiographic changes is essential, since this is a surgically curable lesion.