Diaphragmatic paresis is a rare but recognized complication of atrial fibrillation ablation.A 59-year-old woman experiencing dyspnea in supine position and for minimal effort was admitted in a cardiac rehabilitation center. One month before, she was referred to a cardiac center to ablation of paroxysmal atrial fibrillation. After the procedure, the patient developed respiratory failure attributed to aspiration pneumonia and requiring mechanical ventilation.At admission in the rehabilitation center, M-mode ultrasonography reported an absence of movement of the right hemidiaphragm during quiet breathing and a paradoxical movement during voluntary sniffing.Chest ultrasonography can be useful to detect diaphragmatic dysfunction in patients suffering from dyspnea, at admission in a cardiac rehabilitation center. Its use should be envisaged more frequently.