The prognostic values of indices obtained by M-mode and two-dimensional echocardiography (Echo) and by cardiac catheterization (Cathe) were assessed in patients with idiopathic dilated cardiomyopathy. Fifty-one patients with this disorder (38 males and 13 females) were studied for an average of 4.2 years. Of those, 24 died of cardiac causes during follow-up. The overall 5-year survival rate was 49%. Significant differences between the surviving patients and the patients who died were noted in the following indices measured by Cathe: left ventricular end-diastolic volume (LVEDV), left ventricular end-diastolic pressure (LVEDP), ejection fraction (EF), and the cardiac index (CI). The 5-year survival rate in patients with the following index values measured by Cathe at the initial examination were: LVEDV greater than or equal to 150 ml/M2 - 29%; LVEDP greater than 12 mmHg - 35%, EF less than 30% - 21%, and CI less than 3.0 L/min/M2 - 29%. In contrast, the 5-year survival rate in patients with the following parameter values measured by Echo were: left ventricular end-diastolic dimension greater than or equal to 45 mm/M2 - 16%; left atrial dimension greater than or equal to 25 mm/M2 - 12%; ejection fraction less than 30% - 31%; and a relative wall thickness (a ratio of left ventricular posterior wall thickness to left ventricular end-diastolic dimension) less than or equal to 0.12 - 9%. In assessing the cumulative survival rate, the indices provided by Echo revealed similar values when compared with those obtained by Cathe. The relative wall thickness determined by Echo would be the most reliable parameter for forecasting the 5-year survival rate.(ABSTRACT TRUNCATED AT 250 WORDS)