Fluid and electrolyte management post-cardiac surgery is paramount for optimizing patient recovery and mitigating perioperative complications. This chapter reviews normal fluid and electrolyte distribution in the body; and explores comprehensive strategies to address disruptions in fluid balance, electrolyte concentrations, and acid–base equilibrium that commonly occur after cardiac surgery. The physiological alterations induced by procedures such as cardiopulmonary bypass (CPB) necessitate meticulous planning to maintain hemodynamic stability and organ perfusion. Common postoperative disturbances include hypokalemia, hyponatremia, and fluid overload, each contributing to risks such as arrhythmias, myocardial dysfunction, and prolonged ventilatory support. Effective management revolves around evidence-based approaches, including the judicious selection of fluid type—crystalloids versus colloids—and the implementation of goal-directed therapy to customize care based on individual patient conditions. This entails continuous hemodynamic monitoring and dynamic assessment of fluid status, which are critical in tailoring interventions to enhance outcomes and facilitate early mobilization. The pathophysiological basis of fluid and electrolyte shifts post-surgery will be discussed, and the importance of integrating regular electrolyte monitoring and balanced fluid administration to prevent complications such as acute kidney injury and capillary leak syndrome will be highlighted. The chapter also addresses the financial factors influencing research in fluid management, which often complicate the clinical application of research findings. With a critical review of current evidence and a discussion on the debated practices in fluid management, the chapter provides a framework for understanding and addressing the complex needs of cardiac surgery patients. By consolidating physiological insights and clinical guidelines, it aims to equip healthcare providers with the knowledge to optimize fluid and electrolyte balance, thereby improving the quality of care and patient outcomes in the cardiac surgical setting.