b. prevent the heart from filling properly with blood
The pericardial cavity is the cavity present between the visceral pericardium and the parietal pericardium. It is filled with a fluid called pericardial fluid. In cardiac tamponade, there is an accumulation of excess of the fluid in the pericardial cavity.
The fluid builds up the pressure which in turn compresses the heart. Ventricles of the compressed hearts are not completely filled with blood resulting in reduced cardiac output. Similarly, the return of blood to the heart atria via veins is also reduced in the compressed heart.
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