Final answer:
Pericardiocentesis is the medical procedure used to remove fluid from the pericardial sac, helping to alleviate the dangerous condition known as cardiac tamponade.
Step-by-step explanation:
The procedure that removes fluid from the pericardial sac, a condition known as cardiac tamponade, is called pericardiocentesis. During this procedure, a needle and a catheter are used to drain the excess fluid from the pericardial cavity. By doing so, pressure on the heart is relieved, and the heart can relax properly and fill with blood for the next contraction. This is crucial because untreated cardiac tamponade can lead to decreased cardiac output and potentially be fatal.