Contrary to common belief, the primary cause of acute kidney injury in patients presenting to emergency departments with heart failure is not diminished renal perfusion but rather renal venous congestion and increased pressure. In patients without overt signs of heart failure during initial physical assessment, however, congestion often cannot be distinguished through physical examination alone, leading to congestive nephropathy being frequently overlooked in the differential diagnosis of worsening renal function. Physicians often avoid diuretics for fear of exacerbating renal impairment and instead opt for fluid replacement. This approach can further deteriorate renal function. We describe the clinical course of a patient with heart failure and impaired renal function whose diagnosis of congestive nephropathy was initially overlooked. A 68-year-old male with a history of heart failure, pulmonary hypertension, and chronic obstructive pulmonary disease was admitted to the cardiovascular surgery service for deep vein thrombosis and acute kidney injury. His physical examination upon admission revealed a blood pressure of 135/85 mmHg. Lung sounds were diminished in the basal zones, with expiratory rhonchi and wheezing in the mid-zones, consistent with his underlying pulmonary disease. The cardiac examination was unremarkable. The lower extremity affected by deep vein thrombosis was locally swollen and erythematous, while the other limb had no edema. His oral mucosa and the dorsum of his tongue were dry. With a creatinine level of 1.3 mg/dL (baseline: 0.9 mg/dL), his condition was assessed as prerenal acute kidney injury because the initial physical findings showed no evidence of hypervolemia; consequently, fluid replacement was administered. On the third day, after his renal function further deteriorated, a nephrology consultation was requested. At this time, his physical examination revealed prominent signs of hypervolemia and symptoms of heart failure. Intravenous furosemide was initiated on the fourth day. Renal function improved rapidly after discontinuing fluid replacement and initiating diuretic therapy. Differential diagnoses for patients with heart failure presenting with impaired renal function should include dehydration, as well as drug- and infection-related kidney injury. Congestive nephropathy can develop in all forms of heart failure and should therefore be considered in patients with unexplained renal dysfunction. Proper management of congestive nephropathy is associated with fewer long-term hospital readmissions for heart failure and improved survival rates. In ambiguous cases, the differential diagnosis can be established through point-of-care ultrasonography or, when unavailable, a diagnostic fluid challenge.