A 66-year-old man with known metastatic carcinoid tumor presented with increasing dyspnoea, right heart failure and marked hypoxaemia which did not correct with oxygen. Echocardiography demonstrated severe tricuspid regurgitation, moderate pulmonary regurgitation and marked right heart dilatation. The inter-atrial septum was aneurysmal, with a large patent foramen ovale (PFO) with continuous right to left shunting. Cardiac catheterization demonstrated oxygen saturations of 96 in the pulmonary veins and 74 in the left atrium with a significant right to left shunt. During percutaneous closure of the PFO, anaesthetic induction resulted in marked systemic hypotension and worsening hypoxia related to systemic vasodilatation and increased shunting. PFO flow was temporarily obstructed with a sizing balloon resulting in a rapid increase in arterial oxygen saturation from 60 to >90 , but marked systemic hypotension due to acute left ventricular preload reduction, requiring volume replacement and adrenaline. Following deployment of a PFO occluder device, prominent pulsatile splaying of the right and left discs was noted due to the severe tricuspid regurgitation, resulting in some residual inter-atrial shunting. Arterial oxygen saturation was 83 , increasing to 92 at day 4 post-procedure as tissue organization occurred within the device, and the patient reported improvement in dyspnoea.