Martens P, et al. - In this study with prospectively included patients with stable chronic heart failure (HF; n=80) and either reduced or preserved ejection fraction, researchers investigated the link between urinary sodium (U_na) concentration and the pathophysiologic interaction with the development of acute heart failure (AHF) hospitalization. For 30 consecutive weeks, participants (71 ± 11 years of age) prospectively submitted morning spot U_na samples. The longitudinal shifts in U_na concentration were evaluated using linear mixed modeling. They found that U_na concentration continued to be relatively stable over time; however, the existence of large interindividual differences was reported in stable chronic HF patients. A chronically lower U_na concentration and a further decline in U_na concentration during the week preceding hospitalization was observed in patients who developed AHF. Findings demonstrated the feasibility of ambulatory U_na sample collection, as well as the possible utility of it in providing additional prognostic and therapeutic information.