The correct management of acute heart failure continues to pose diagnostic and therapeutic challenges. In particular, administering the right type and dose of fluids and drugs, thus avoiding fluid overload while establishing organ perfusion, is of key importance in stabilizing critical patients and improving prognosis. A correct estimate of the fluid volume status, however, may be difficult, as the invasive evaluation of cardiac filling pressures by cardiac catheterization is limited in routine medical practice, and there is no universal consensus on the best tools for its non-invasive evaluation. Here we review current evidence about diagnosis and treatment of fluid volume abnormalities in acute heart failure according to the most recent guidelines.