Answer: Pulmonary vein stenosis is the narrowing of the pulmonary veins. This can happen occasionally in patients after AF ablation. If the narrowing is severe > 70% and affects two veins on the same side they can impede blood return from the lung on that side of the chest. This can result in symptoms of shortness of breath, fatigue, coughing, blood in sputum. PV stenosis used to be a frequent problem during the early years of AF ablation when the radiofrequency lesions were placed either deep inside the vein or just at the opening of the vein. As the electrophysiology community realized this problem, the ablation points moved away from the opening of the vein. The current strategies involve doing circular lesions farther away from the opening either in the funnel portion (antral) of the vein are in the atrial body. The closer the lesion set is to the opening better is the confidence in the isolation of the veins. The farther we move away from the opening of the vein the more difficult it gets to completely isolate the vein. The current rates of PV stenosis range from 2-5% depending on the technique. CT or MRI of the heart are done to monitor for the PV diameters before and after the AF ablation. Any degree of stenosis should be followed by repeat CT or MRI scans to assess for progression of the stenosis. Ventilation/perfusion scans help to assess the physiologic impact of the stenosis on the lung perfusion. Pulmonary vein angioplasty and stenting are helpful in mitigating symptoms in patients with significant stenosis.