"Cardio-renal syndromes" (CRS) are disorders of the heart and kidneys whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction of the other. The current definition has been expanded into five subtypes whose etymology reflects the primary and secondary pathology, the time-frame and simultaneous cardiac and renal co-dysfunction secondary to systemic disease: CRS type I: acute worsening of heart function (AHF-ACS) leading to kidney injury and/or dysfunction. CRS type II: chronic abnormalities in heart function (CHF-CHD) leading to kidney injury or dysfunction. CRS type III: acute worsening of kidney function (AKI) leading to heart injury and/or dysfunction. CRS type IV: chronic kidney disease (CKD) leading to heart injury, disease and/or dysfunction. CRS type V: systemic conditions leading to simultaneous injury and/or dysfunction of heart and kidney. These different subtypes may have a different pathophysiological mechanism and they may represent separate entities in terms of prevention and therapy.