Cardiorenal syndromes refer to clinical and metabolic consequences of acute and chronic heart failure or kidney disease on other organ. Recent studies have further clarified the pathophysiological mechanisms behind the different types of cardiorenal syndromes and propose a new classification. The cardiorenal syndrome type 1 corresponds to an acute heart failure (cardiogenic shock, acute decompensated congestive heart failure) which induces acute renal dysfunction. In the cardiorenal syndrome type 2 heart failure is chronic (congestive heart failure) and induces chronic kidney damages in the long-term. Whereas the renocardiac syndrome type 3 (acute) or 4 (chronic) corresponds to either acute renal failure situation (acute renal failure with tubular necrosis secondary to acute collapsus...) responsible for acute heart failure (left ventricular failure and pulmonary edema) or chronic (chronic glomerulonephritis, polycystic...) leading to chronic heart alteration (left ventricular hypertrophy, heart failure, arrhythmias). Finally, the failure of both organs can be simultaneous and secondary to a systemic or a metabolic disease (amyloidosis, diabetes) and corresponds to cardiorenal syndrome type 5. Epidemiological studies highlight the high incidence of cardiorenal syndromes type 1 and 2 and particularly the deleterious impact of renal impairment on the short and medium-term prognosis of heart failure. This classification is of essential interest for better identification of patients and help for the development of therapeutic studies.