Clinical introduction A 17-year-old boy with primary cardiac diagnosis of cor triatriatum, atrial septal defect (ASD) and patent ductus arteriosus (PDA) was referred for a cardiac MRI. He was operated on at 3 months of age with correction of the above-mentioned defects. During follow-up, on echocardiogram, he gradually developed moderate right ventricular dilation with preserved systolic function and a trace of tricuspid regurgitation. The interatrial septum was intact and the left chambers looked normal in size (see online supplementary video 1). Clinically, he was active and asymptomatic with saturations of 99% on air. Consequently, he was referred for an MRI scan to look for possible causes. The images are seen in figure 1.

Question What diagnosis would you suspect from figure 1?

1. Arteriovenous malformation

2. Left superior vena cava

3. Levoatriocardinal vein

4. Meandering pulmonary vein