The pericardial space normally contains several ml of serous fluid. Due to diseases and external or iatrogenic trauma, the fluid volume may increase, either acutely or chronically. The increase of volume and intrapericardial pressure may compress cardiac chambers and restrict filling, which may lead to a decrease in cardiac output and cardiac tamponade. Rapid accumulation of pericardial fluid may produce tamponade at much smaller volumes than when accumulation occurs over a longer period of time.