Cardiac tamponade is an insidious and often fatal complication which can occur on any service, in many diseases, and at any age. The increasing pressure within the pericardium prevents ventricular filling and depresses cardiac output, coronary and systemic perfusion, and venous return. Compensatory mechanisms may protect the patient for some time, but prompt diagnosis and rapid decompression are usually required and must be followed by meticulous evaluation and treatment of the underlying disease.