Purpose Angiotensin-converting enzyme inhibitors (ACEI) and angiotensin receptor blockers (ARB) were shown to improve the prognosis of patients with acute decompensated heart failure (ADHF) and depressed left ventricular systolic function (DLVSF). Recently, elderly patient ���65 years became a main group of ADHF. Clinical impact of ACEI or ARB in this patients group has been rarely evaluated in Korea. Method The Korean Acute Heart Failure (KorHF) Registry enrolled 3,200 patients with ADHF from Nov 2005 to Nov 2009 in South Korea. From KorHF Registry, 1,336 elderly patients ���65 years and DLVSF (EF <50%) were included in this study. They were divided into two groups; neither ACEI nor ARB (group 1; n=361, 27%) and either ACEI or ARB (group 2; n=975, 73%) during the index admission. Results Age and sex ratio were not different. Initial systolic BP was lower in group 1. Patients in group 1 had more history of myocardial infarction and chronic kidney disease. The main underlying heart disease was ischemic heart disease in both groups (48% vs. 47%), but patients in group 1 had less dilated cardiomyopathy (11% vs. 20%, p<0.001). Initial NYHA functional class was not different. Serum BUN, creatinine was higher in group 1. Left ventricular ejection fraction was less depressed in group 1. Beta-blockers were similarly used in both groups, but spironolactone was less frequently used in group 1 (17% vs. 39%, p<0.001). Patients in group 1 had lower 1-year survival rate (77.8% vs. 86.6%, p<0.001), and 1-year event-free survival rate (62.1% vs. 69.4%, p=0.009). On multivariate analysis, use of either ACEI or ARB was a strong predictor of survival (OR 0.60, 95% CI 0.43-0.84, p=0.003). Conclusions Either ACEI or ARB was not used in a quarter of elderly patients with DLVSF. Their long-term outcomes may be improved by the more selected use of ACEI or ARB.