Air embolism secondary to mechanical ventilation is a rare but well-described complication in premature infants. We describe the echocardiographic appearance of venous air embolism manifesting as acute obstruction of the right ventricular outflow tract in such a premature infant, and review the pathophysiology of acute obstruction of the right ventricular outflow tract secondary to the "air lock" phenomenon. Awareness of the pathophysiology and echocardiographic appearance of venous air embolism may aid in prompt recognition and potential therapy for this lethal complication of mechanical ventilation.