Monoclonal 111In antimyosin (AMS) uptake indicates the presence of ongoing myocyte damage. In idiopathic dilated cardiomyopathy (IDC), there is diffuse myocyte damage. We have attempted to find a correlation between AMS uptake and functional myocardial parameters. With this purpose in mind, we studied two groups of subjects: group 1 comprised 19 subjects with IDC and group 2 comprised 6 control subjects. In all subjects, an antimyosin scan was performed. Among the subjects with IDC, two-dimensional echocardiography was carried out to determine the left ventricular ejection fraction (LVEF) and left ventricular dimensions, and a gated blood pool study was undertaken to assess the LVEF at rest and end-diastolic and end-systolic volumes. Three months later, repeat antimyosin scintigraphy and equilibrium gated blood pool were performed on 13 of the patients. The mean heart to lung (H/L) ratio in the IDC subjects was 1.82 +/- 0.25 (range 1.42-2.25), a value significantly higher than that obtained in the controls: 1.41 +/- 0.12 (range 1.26-1.58) (P < 0.001). Linear regression analysis did not find a statistically significant correlation between H/L and gated blood pool or echocardiography measures. No marked changes in ejection fraction and antimyosin uptake were found between baseline and follow-up studies. Subjects with IDC have a high incidence of positive antimyosin scans, but antimyosin uptake is not related to any functional or morphological parameters.