Subclavian vein cannulation is frequently performed in patients undergoing electrophysiologic procedures in order to facilitate catheterization of the coronary sinus. We present a rare case of massive haemothorax, secondary to subclavian artery injury, during an ablation of atrial fibrillation. Following the procedure, a chest radiograph revealed a massive left haemothorax and the angiographic phase of a computed tomography scan indicated the presence of active bleeding due to left subclavian artery injury. Active bleeding was initially managed through embolization of the subclavian artery branches and the patient was subsequently treated with combined endovascular stenting and video-assisted thoracic surgery.