OBJECTIVES: The present study was designed to determine if patients with an echocardiographic diagnosis of idiopathic dilated cardiomyopathy should be submitted to coronary arteriography. BACKGROUND: Whether echocardiography allows distinction of idiopathic dilated cardiomyopathy from severe coronary heart disease remains controversial. METHODS: A questionnaire was sent out to the members of the Swiss Society of Cardiology. In the first study 78 patients with an echocardiographic diagnosis of idiopathic dilated cardiomyopathy who had undergone coronary arteriography or had been followed-up for >5 years were investigated. In a second study, the echocardiograms of 50 patients with either idiopathic cardiomyopathy or severe coronary heart disease, all of whom had also undergone coronary arteriography, were reviewed by two independent echocardiographers without access to any complementary information. RESULT: The questionnaire revealed that one half of the Swiss cardiologists generally refer such patients for coronary arteriography. The first study showed that the diagnosis of idiopathic dilated cardiomyopathy was confirmed in all cases, in which the echocardiographer had been certain of the diagnosis (64/78 [82%]). In the uncertain cases (14 [18%]) coronary arteriography revealed 9 idiopathic cardiomyopathies, 3 coronary heart diseases, and 2 mixed etiologies. The second study showed that a correct diagnosis was achieved in 85% of cases. Furthermore, the echocardiographers were able to specify those patients with an uncertain diagnosis who would therefore require coronary arteriography. CONCLUSIONS: In the overwhelming majority of cases, echocardiography can distinguish idiopathic dilated cardiomyopathy from severe coronary heart disease. Coronary arteriography is only indicated when the echocardiographer is uncertain of the diagnosis. The routine and costly practice of coronary arteriography of these patients does not appear to be justified.