Pericardial tamponade limits diastolic filling of the heart; therefore, a high venous pressure is required to fill the ventricle. In presence of cardiac tamponade, therapeutic agents and manoeuvres that results in venodilation or vasodilation can severely compromise diastolic filling of the heart and might result in rapid cardiac decompensation. Equalization of central venous pressure and pulmonary artery diastolic pressure or equalization of pressures in all four chambers during diastole confirms cardiac tamponade. Transthoracic echocardiography can detect the site of tamponade and assist in pericardiocentesis. We describe acute pericardial tamponade in a young man who underwent left posterolateral thoracotomy for left upper lobectomy. Intraoperatively, mobilization of the left upper lobe was frequently associated with hypotension. Postoperatively, the patient suffered two more episodes of hypotension. The episodes of hypotension were attributed to surgical manipulation and epidural blockade. Hemodynamics normalized after discontinuing epidural infusion, volume resuscitation and lobectomy. On third postoperative day, the patient developed cardiovascular collapse; arterial blood pressure and central venous pressure were 70/50 and 12 mmHg. Investigations showed haziness of left lung, and severe respiratory acidosis. On opening of the left thoracotomy wound, pericardial tamponade was diagnosed. A pericardial window was created and tamponade was released with that the hemodynamics normalized. Episodes of unexplained hypotension after left upper lobectomy suggest a cardiac etiology and acute pericardial tamponade is a possibility which should be released immediately otherwise it can result in fatal outcome.