In order to evaluate the incidence of myocardial ischaemia in patients who developed acute pulmonary oedema during the immediate post-operative period, continuous monitoring of the electrocardiogram by the Holter method was used in 200 consecutive patients with coronary artery disease. Fourteen of these patients exhibited ST segment depression during the post-operative period and 13 during surgery. Nine patients developed acute pulmonary oedema immediately after the operation and in 7 cases the oedema was preceded by myocardial ischaemia. A continuous nitroglycerin infusion brought about regression of the pulmonary oedema in 8 cases. One patient died despite treatment. These findings underline the part played by myocardial ischaemia in the pathogenesis of acute post-operative pulmonary oedema in patients with coronary artery disease.