1. The circulatory response to supine exercise and to angiotensin infusion was measured in patients with chronic obstructive pulmonary disease (COPD).

2. Left ventricular function assessed from left ventricular end-diastolic pressure (LVEDP)-stroke volume or stroke work relationships was almost always normal in the patients without cardiac failure. The patients with right heart failure showed an abnormal response with a pronounced rise of LVEDP during both exercise and infusion of angiotensin. The values of LVEDP showed a significant correlation with RVEDP and with arterial oxygen saturation and carbon dioxide tension under both experimental conditions. No abnormality in the response of cardiac output, mean systolic ejection ratio or systolic ejection time was observed. In thirteen out of fifteen patients subjected to both exercise and infusion of angiotensin, the results of the two tests agreed in showing left ventricular function to be normal or abnormal; two patients showed an abnormal response to exercise, but a normal response to angiotensin.

3. The possible causes of the abnormality of left ventricular function in COPD with right heart failure are discussed. Changes in left ventricular compliance and the effect of chronic hypoxaemia and hypercapnic acidosis on myocardial contractility seem to be the most probable explanation.

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