Cardiac tamponade occurs when fluid (e.g. blood) accumulates in the pericardial space between the pericardium and the myocardium of the heart. Since the pericardial sac is inflexible, the accumulating blood presses on the heart. This prevents adequate filling of the ventricles and cardiac output is diminished. The treatment for cardiac tamponade is pericardiocentesis in which a needle is inserted into the pericardial space to drain the fluid and decompress the heart. An ultrasound is often used for this purpose. A chest tube is placed across the chest wall to treat pneumo- or hemothorax. Coronary artery bypass and percutaneous intervention are performed to treat coronary artery disease.