Final answer:
Pericarditis causes a reduction in cardiac output due to fluid accumulation in the pericardial cavity, which puts pressure on the heart and prevents it from fully relaxing.
Step-by-step explanation:
Pericarditis causes a reduction in cardiac output due to the accumulation of fluid in the pericardial cavity, a condition known as cardiac tamponade. The excess fluid puts pressure on the heart and prevents it from fully relaxing, resulting in less blood being ejected from the heart with each contraction. Over time, this leads to a decrease in the overall amount of blood pumped by the heart. Rapid accumulation of fluid or inflammation from infections can also contribute to the reduction in cardiac output.