Ultrafiltration has been used in patients with decompensated HF and volume overload refractory to diuretics. Criteria for the initiation of renal replacement therapy (RRT) in the ICU are oliguria, anuria, urea, creatinine, Na and K blood concentrations, pulmonary edema unresponsive to diuretics, uncompensated metabolic acidosis, temperature >40°C, uremic complication, and overdose with a dialyzable toxin. Moreover, the treatment of acute renal failure requires a different style and philosophy from renal replacement therapy for chronic renal failure. The degree and the location of renal lesion, the entity, the gravity of the concomitant acute or chronic cardiac damage, the weight of a trauma, surgical stress, or septic complication they determine a variability of clinical picture that can modify the prescription and the timing of RRT and the monitoring technology. In the presence of cardiac alterations due to a condition of chronic heart failure, all the acute events contribute to the progression of the cardiac insufficiency and the patient will always have as a result an ulterior reduction in the cardiac function. It derives the opportunity to put more precociously in action everything of it how much serves for a real cardioprotection. A valid hemodynamic monitoring is essential to reach the lowest possible value of pressure of left ventricular filling, without reduction in the cardiac output, increase in the cardiac frequency or the ulterior activation of the neurohormones. An early ultrafiltration allows a more easy control of the circulating mass but also an effective neurohormonal purification and of all the inflammation mediators.