Fluid administration is a powerful tool for hemodynamic stabilization as it increases preload and improves cardiac function in fluid-responsive patients. However, there are various types of fluid to choose from. The use of colloids and crystalloids in non-cardiac Intensive Care Units (ICU) has been reported, showing controversial results. Many trials on sepsis in a non-cardiac ICU setting show that colloids, in particular hydroxyethyl starches and gelatins, might have a detrimental effect on kidney function, and on major outcomes such as mortality. Many small randomized clinical trials focusing on coagulation and bleeding show controversial results regarding fluid safety during the perioperative period in cardiac surgery, and in the cardiac ICU. No definitive data are available on the superiority of one fluid compared with another for fluid replacement after cardiac surgery. Only few data are available regarding the impact of fluids on kidney function in the cardiac ICU. On the other hand, there is much evidence showing that fluid administration requires strict protocols and close monitoring. Improved clinical outcomes are evident in protocols for goal-directed therapy. In conclusion, the application of a close monitoring and a pre-defined goal-directed protocol are far more important than the choice of a single fluid. This review examines the available evidence on fluid management in cardiac surgery and in the ICU, and analyzes the key steps of fluid strategy in these settings.