Renal dysfunction affects approximately 30 to 50% of heart failure (HF) patients. The unfavourable relationship between heart and kidney dysfunction contributes to worse outcomes through several mechanisms such as inflammation, oxidative stress, impaired hydrosaline homeostasis, and diuretic resistance. Renal dysfunction not only carries important prognostic value both in acute and in chronic HF, but also is a potential precipitating factor after the first diagnosis. Because renal dysfunction encompasses different etiologies, a better understanding of its definition, incidence, and pathophysiology provides additional information. Although old and novel available biomarkers for the detection of renal dysfunction have been recently proposed, there is no general consensus regarding the terminology and definition of renal dysfunction in HF. Due to some specific pathophysiological mechanisms, renal impairment seems to be different on an individual patient level and, recognizing it in acute and chronic settings, could be useful to optimize decongestive treatment. For these reasons, in this review, we aim to describe and evaluate different phenotypes of renal dysfunction in acute and chronic HF and the possible management in these settings.

• Chronic kidney dysfunction and worsening renal function are highly prevalent in acute heart failure and chronic heart failure and associated with poor outcomes.

• This association is modified by the context in which it occurs, i.e. worsening renal function in the context of adequate decongestion in acute heart failure, or worsening renal function after initiation of neurohormonal blockers in chronic heart failure.

• Future research should be aimed at elucidating the mechanisms involved in these differenct contexts, as well as alternative treatment approaches in the case of true worsening renal function.