Acute kidney injury (AKI) occurring during heart failure (HF) has been labelled cardiorenal syndrome (CRS) type 1. CRS is defined as a group of ‘disorders of the heart and kidneys whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction of the other’. This consensus definition was proposed by the Acute Dialysis Quality Initiative, with the aim to standardize those disorders where cardiac and renal diseases coexist. Five subtypes have been proposed, according to which organ is affected first (cardiac vs renal) and whether the dysfunction is acute or chronic. Another subtype which includes systemic conditions leading to both heart and kidney dysfunction is also described.The term ‘worsening renal function’ has been regularly used to describe the acute and/or subacute changes that occur in the kidneys following HF. However, the AKI classification according to the current consensus definition better represents the entire spectrum of AKI in the setting of HF.The pathophysiology of heart–kidney interaction is complex and still poorly understood. Factors beyond the classic haemodynamic mechanisms appear to be involved: neurohormonal activation, venous congestion, and inflammation have all been implicated.Diuretics are still a cornerstone in the management of HF. Intravenous administration by bolus or continuous infusion appears to be equally efficacious. Biomarkers and bioelectrical impedance analysis can be helpful in estimating the real volume overload and may be useful to predict and avoid AKI. The role of ultrafiltration remains controversial, and it is currently recommended only for diuretic-resistant patients as it has not been associated with better outcomes. The occurrence of AKI during HF is associated with substantially greater short- and long-term mortality.