Diuretic resistance portends a poor prognosis in acute heart failure, especially in advanced stages. Early identification of a poor response to diuretics may help to improve treatment and outcomes. Spot natriuresis (UNa+) at 2 h from the start of intravenous furosemide has been proposed as an early indicator of diuretic response. Our paper aimed to determine the role of early natriuresis in patients hospitalized with advanced chronic heart failure (ACHF) and high risk of diuretic resistance.