Fluid overload is often observed in patients with heart failure and secondary oliguric states. A thorough assessment of the fluid status of the patient may help guide the therapy and prevent complications induced by inappropriate therapeutic strategies. The present publication is divided into four parts: Definition and Classification, Pathophysiology, Diagnosis and Therapy. In the first section, the authors present new definitions for heart failure, acute kidney injury and cardiorenal syndromes to facilitate the process of understanding the complex link between the heart and the kidney. Subsequently, different conditions leading to fluid overload are described, followed by an account of emerging diagnostic tools, therapies and technologies devoted to the treatment of patients with severe fluid-related disorders. Clearly structured and written, the present book is a practical tool for physicians and professionals involved in the management and care of patients with combined heart and kidney disorders. Moreover, it also serves as a reference textbook for medical students, residents and fellows dealing in everyday practice with fluid overloaded and oliguric patients.