Cardiac tamponade is a life-threatening condition caused by fluid under pressure around the heart.
The heart lies inside a tissue sac called the pericardium. Fluid that collects in the pericardial sac can develop enough pressure to prevent the heart from relaxing completely between beats. The pressure prevents complete filling of the heart before the next heartbeat. This lessens the amount of blood that can be pumped by the heart. Severe pericardial fluid pressure can cause a drop in blood pressure, shock, abnormal heart rhythms, and death.