Ten minutes after the procedure the patient complained of pain in the left infrascapular region. A chest radiograph revealed patchy opacification in the left mid and lower zones of the lung fields ( Fig. 1) but clinical examination of the chest was normal. She maintained satisfactory progress until seven hours after the procedure when she collapsed with tachypnoea, tachycardia, hypotension, and signs of a large left pleural effusion. A chest radiograph confirmed a pleural effusion on the side of the cannulation (Fig. 2). Intrathoracic bleeding was diagnosed and after rapid blood transfusion emergency thoracotomy was performed.At operation 4 litres of blood were evacuated from the left hemithorax. A puncture site was noted in the left subclavian vein, and at the corresponding position on the apex of the left lung a branch of the pulmonary artery was bleeding profusely. A few fibrous pleural adhesions were present on the apical pleura and the indwelling catheter was found to be in the lumen of the left subclavian vein. Haemostasis was secured and the patient made good postoperative progress.