Pleural lavage with distilled water is often employed in lung resection to eliminate malignant cells. Here we report a case of transient ST segment elevation on electrocardiogram (ECG) during pleural lavage with distilled water. A 73-year-old female was referred to our hospital because of an abnormal shadow on a chest roentogenogram. Chest computed tomography scan revealed a mass in left S4+5 segment of left upper lobe. It was proved to be adenocarcinoma of the lung by transbronchial lung biopsy and she underwent left upper lobectomy. During pleural lavage with distilled water, ST segment was elevated on ECG. In this case, it was because that the pericardium was excised and the myocardium was exposed to distilled water during pleural lavage.