Dilated cardiomyopathy was observed in 2 patients with chronic obstructive lung disease. This association raises first a diagnostic problem: the low specificity of clinical, radiographic and electrocardiographic signs makes it difficult to diagnose a left ventricular failure in such patients. Echocardiography is useful, but right and left heart catheterization and coronary arteriography are needed to establish the diagnosis of dilated cardiomyopathy and exclude other causes of left cardiac failure. The cause-effect relationship between the 2 diseases is not easy to evaluate. It is studied here in the light of the different mechanisms suggested to explain the repercussions function and notably the interactions between ventilation and right and left ventricular function. However, the association of the 2 diseases seems to be fortuitous. Their reciprocal repercussions, notably in the field of haemodynamics, are unquestionable and make the overall prognosis worse.