In the CONSENSUS study, M-mode echocardiography was used as an optional examination. All patients were in severe congestive heart failure [New York Heart Association (NYHA) functional class IV], and all patients had radiologically marked increased heart size. Of 253 patients, M-mode echocardiography was done at baseline in 105 patients. M-mode echocardiographic recordings from 70 patients were received, and of these, only 54 patients (77%) had recordings of acceptable quality for evaluation. At follow-up, M-mode echocardiography was done after 6 weeks, 6 months and 12 months. However, because of the high mortality and the premature cessation of the study, only a limited number of patients had M-mode echocardiographic registrations after greater than 6 weeks. All M-mode echocardiographic registrations were analysed by 2 investigators independently. Systolic time interval (STI) decreased from 0.58 to 0.48 (p less than 0.05) in the enalapril group after 6 weeks. In the placebo group, a small increase in STI from 0.54 to 0.56 (not significant) was seen after 6 weeks. The decrease in STI in the enalapril group was secondary to an increase in left ventricular ejection time. No significant change was seen in left ventricular and left atrial diameters at follow-up: this finding can be explained by a type 2 error. These findings indicate an increased STI in the enalapril-treated group, which could explain why enalapril treatment reduced mortality in the CONSENSUS study.