The patient's presentation with hypotension, distended neck veins, and muffled heart sounds constitutes Beck's triad, which is pathognomonic for cardiac tamponade. This condition occurs when fluid accumulates in the pericardial sac, leading to increased intrapericardial pressure that restricts cardiac filling during diastole. The resulting decreased stroke volume causes hypotension. Distended neck veins reflect impaired venous return, and muffled heart sounds result from the fluid buffer around the heart. Prompt surgical intervention, such as pericardiocentesis or surgical pericardial window, is critical to relieve pressure and restore cardiac output.

Reference: Tintinalli's Emergency Medicine: A Comprehensive Study Guide, Judith E. Tintinalli, 9th Edition.