BACKGROUND : Radiofrequency catheter ablation is approved effective therapy for premature ventricular contraction. However, the rare but serious complication such as pseudoaneurysm should be given more attention. It is life-threatening due to the high risk of rupture. Only few cases have been reported in the literature. We herein report a huge acute left ventricular pseudoaneurysm after catheter ablation therapy. METHODS : A 69-year-old man underwent radiofrequency catheter ablation for premature ventricular contraction at a local hospital. The patient developed shock the second day after ablation. A chest computed tomography (CT) scan showed pericardial effusion. Pericardiocentesis was performed, and the puncture fluid was a bloody pericardial effusion. The transthoracic echocardiogram revealed an 9- × 4-cm giant pseudoaneurysm with a cystic structure in the left ventricular inferior wall near the mitral annulus along the left atrium. The pseudoaneurysm was connected to the left ventricular cavity through a 8-mm neck, and the lumen was filled with systolic and diastolic blood flow. The patient underwent three-dimensional transesophageal echocardiography. The pseudoaneurysm and the tract was clearly visible. Emergency surgery was performed to resect the pseudoaneurysm. A bovine pericardial patch was placed on the neck of the pseudoaneurysm. Echocardiographic examination confirmed the absence of cardiac lesions after the operation. CONCLUSIONS : It is rare to see such a large pseudoaneurysm after radiofrequency catheter ablation. Clinicians should be allert to the potential risks to patients in the process of an effective treatment. Echocardiography plays an important role in the prompt diagnosis and prognosis of this disease. Emergency surgery is a better method for treatment of huge pseudoaneurysm.