Background:Microalbuminuria, traditionally defined as urinary albumin/creatinine ratio (UACR) ≥30 mg/g, is a risk factor for mortality even in patients with preserved glomerular filtration rate (GFR). The prognostic impact of subclinical microalbuminuria, however, remains unknown in patients with chronic heart failure (CHF).Methods and Results:In the Chronic Heart Failure Analysis and Registry in the Tohoku District 2 Study, we enrolled 2,039 consecutive symptomatic CHF patients (median age, 67.4 years; 68.9% male) after excluding those on hemodialysis. On classification and regression tree analysis, UACR=10.2 mg/g and 27.4 mg/g were identified as the first and second discriminating points to stratify the risk for composite of death, acute myocardial infarction, HF admission and stroke, therefore subclinical microalbuminuria was defined as UACR ≥10.2 and <27.4 mg/g. There were 506 composite endpoints (24.8%) during the median follow-up of 2.69 years. On Kaplan-Meier analysis and multivariate Cox modeling, subclinical microalbuminuria was significantly associated with increased composite endpoints with hazard ratios of 1.90 (P<0.001) and 2.29 (P<0.001) in patients with preserved (>60 ml·min-1·1.73 m-2, n=1,129) or mildly reduced eGFR (30-59.9 ml·min-1·1.73 m-2, n=789), respectively. In patients with severely reduced GFR (eGFR <30 ml·min-1·1.73 m-2, n=121), >80% had microalbuminuria or macroalbuminuria, and only 9.1% were free from any composite endpoints.Conclusions:Subclinical microalbuminuria was associated with increased risk of cardiovascular events in CHF patients with mildly reduced or preserved renal function.