Cardiac and kidney diseases are very common, and increasingly coexist. Classification for cardiorenal syndrome and for its specific subtypes has been developed and published recently by a consensus group of the Acute Dialysis Quality Initiative. Cardiorenal syndromes have been classified according to whether the impairment of each organ is primary, secondary or whether heart and kidney dysfunction occurs simultaneously as a systemic disease. The different syndromes were classified into five subtypes. Type-1: acute cardiorenal syndrome: an abrupt worsening of cardiac function leading to acute kidney injury and/or dysfunction. Type-2: chronic cardiorenal syndrome: chronic abnormalities in cardiac function causing kidney injury and/or dysfunction. Type-3: acute renocardiac syndrome: abrupt worsening of kidney function leading to heart injury and/or dysfunction. Type-4: chronic renocardiac syndrome: chronic kidney diseases leading to heart injury, disease and/or dysfunction. Type-5: secondary cardiorenal syndrome: acute or chronic systemic diseases leading to simultaneous injury and/or dysfunction of heart and kidney. The identification of patients and the pathophysiological mechanisms underlying each syndrome subtype will help cardiologists, nephrologists and physicians working on intensive care units to characterize groups of their patients with cardiac and renal impairment and to provide a more accurate treatment for them.