BACKGROUND: Acute decompensated heart failure (ADHF) poses a challenging paradox of renal and cardiac pathophysiology, with volume excess or "congestion" being a key player. Understanding the mechanisms of congestion is crucial for effectively managing fluid overload and improving patient prognosis. SUMMARY: In this review, we evaluate the physiology of congestion and explore its implications for management in clinical practice. Mechanisms of congestion can largely be broken down under the subtext of fluid accumulation and fluid redistribution. Fluid accumulation develops as a consequence of neurohormonal dysregulation, physiologic maladaptive mechanisms, and detrimental crosstalk between the heart and the kidney. On the other hand, fluid redistribution evolves due to progressive overriding of compensatory vascular mechanisms, renal injury, and hormonal feedback. KEY MESSAGES: Understanding the complex pathophysiology of congestion in ADHF is crucial for effective volume management and protection against long-term mortality and morbidity risks. By targeting both fluid accumulation and redistribution mechanisms, clinicians can optimize treatment strategies to alleviate congestion and restore hemodynamic stability in patients with ADHF.