Multi-organ interactions in heart failure pathophysiology have been highlighted. One typical pathophysiology is cardio-renal interaction in adults with congenital heart disease (ACHD) (1). Renal function is evaluated using both the estimated glomerular filtration rate (eGFR) and the presence of albuminuria. In many diseases, such as hypertension, chronic kidney disease, and diabetes mellitus, as well as the general population (2), albuminuria is associated with poor prognosis in a variety of diseases (3,4). Although cyanotic nephropathy has been recognized as a cause of albuminuria in patients with hypoxic ACHD (5), its clinical relevance in terms of its prognostic value of mortality has not been studied in a variety of ACHD patients, including patients with Fontan circulation (FC) (6,7). There is a significant prognostic association between albuminuria and ACHD with biventricular circulation (BVC), whereas the association between albuminuria and adverse outcomes in FC patients has not been well studied (6). To this end, this study aimed to: 1) reconfirm the high prevalence of albuminuria by using the urine albumin-creatinine ratio (ACR) and identify the determinant factors in ACHD based on the hemodynamics; 2) establish the association of albuminuria with all-cause mortality in our large cohort of ACHD patients, and to identify differences in the prognostic values for all-cause mortality between those with FC and BVC.