Diagnostic sensitivity and specificity of cineangiography were evaluated by multivariate logistic discriminant analysis in 32 patients with arrhythmogenic right ventricular (RV) cardiomyopathy, 27 patients with biventricular dilated cardiomyopathy, 28 patients with atrial septal defect and 18 normal subjects. In patients with arrhythmogenic RV cardiomyopathy and biventricular dilated cardiomyopathy, the diagnosis was confirmed by endomyocardial biopsy. All RV values overlapped for the diagnosis of atrial septal defect and arrhythmogenic RV cardiomyopathy; overlapping extended to dilated cardiomyopathy for end-diastolic volume and infundibular dimensions. RV ejection fraction appeared reduced in all the diseases; in particular, mean values in dilated cardiomyopathy and arrhythmogenic RV cardiomyopathy were 38 and 53%, respectively (p less than 0.05). Left ventricular quantitative studies showed a significant difference between dilated and arrhythmogenic RV cardiomyopathy, both in terms of pumping indexes (mean end-diastolic volumes 180 vs 91 ml/m2 and mean ejection fraction 33 vs 60%), and indexes of contractility (stress/end-diastolic volume 3.7 vs 6.7). Multivariate analysis disclosed that transversally arranged hypertrophic trabeculae, separated by deep fissures, were associated with the highest probability of arrhythmogenic RV cardiomyopathy (p less than 0.001). Posterior subtricuspid and anterior infundibular wall bulgings were the only other independently significant variables. Coexistence of these signs was associated with 96% specificity and 87.5% sensitivity. Thus, arrhythmogenic RV cardiomyopathy presents quantitative volumetric and hemodynamic as well as qualitative features that clearly distinguish it from dilated cardiomyopathy and confirm its nosographic autonomy among the primary diseases of the myocardium.