Final answer:
Cardiac tamponade decreases heart sounds due to fluid accumulation in the pericardial cavity, which hinders full heart muscle relaxation and, therefore, reduces the force of heart contractions and sounds produced by valve closures.
Step-by-step explanation:
Cardiac tamponade, a critical condition in which excess fluid accumulates in the pericardial cavity, can result in decreased heart sounds. This is because the fluid build-up puts pressure on the heart, hindering its ability to fully relax and refill with blood between contractions. Consequently, the blood volume inside the heart chambers is reduced, leading to less forceful contractions and fainter sounds when the atrioventricular (AV) and semilunar (SL) valves close. During cardiac tamponade, the compromised cardiac output exacerbates the situation, making the normal "lub-dub" sounds, referred to as S1 and S2, harder to hear via auscultation.