A 13- year-old male presented to us with a history of cyanosis and dyspnea. His two-dimensional transthoracic color Doppler echocardiogram showed a turbulent color jet (A, Online Video 1) from the right pulmonary artery to the left atrium. Contrast echocardiography revealed early dense opacification of the left atrium and the left ventricle with microbubbles (B, Online Video 2) within 2 cardiac cycles. Multidetector computed tomography angiography (lateral view) (C) and three-dimensional volume-rendered computed tomography imaging (D) showed a large (2-cm diameter) fistulous communication between the right pulmonary artery and the left atrium (E, white arrow) with normal peripheral branching of both pulmonary arteries. Subsequent cardiac catheterization and selective right pulmonary arteriogram (left lateral view) delineated the course and waist (15 mm) of the fistula (F, white arrows, Online Video 3). Using a transseptal approach, the Cocoon duct occluder (Vascular Innovations Co., Ltd., Nonthaburi, Thailand) (18 × 20 mm) was successfully deployed (G, black arrows, Online Video 4) across the fistula with no residual shunt (H, Online Video 5).