Cardiac and renal disease are common and frequently coexist, resulting in increased risk of mortality, morbidity and cost of care. The interaction between heart and kidney is refered to as cardiorenal syndrome, but a consensus definition has not been established. Also, there are limited data about the true incidence, the pathophisiology is poorly understood and standardized diagnostic criteria are lacking. Because the process is complex, treatment can be a challenge despite the novel therapies. This paper addresses all the complex interactive aspects of the cardiorenal relationship, from pathophysiology to epidemiology, diagnosis and treatment, to have more clear perspectives on the future therapeutic approaches to this deadly association.