A 4-month-old male infant diagnosed with Pentalogy of Cantrell presented to the cardiac catheterization laboratory with a large pericardial effusion. During an urgent pericardial drain placement, the patient, whose prior hemodynamics and clinical findings had suggested a noncritical cardiac lesion, had a profound desaturation, with echocardiography suggesting minimal or no flow across the right ventricular outflow tract (RVOT). The position of the drainage catheter on fluoroscopy and echocardiography suggested that the spell was being caused by obstruction of the main pulmonary artery (MPA) by the pericardial drain. After partially withdrawing the drain to reposition it, there was immediate resolution of the hypoxemia, and echocardiography once again showed adequate flow across the outflow tract.