Which condition describes inflammation in the sac surrounding the heart, characterized by chest pain?

Pericarditis is the correct answer because it specifically refers to the inflammation of the pericardium, which is the fibrous sac surrounding the heart. This inflammation can lead to a variety of symptoms, with chest pain being one of the most prominent. The pain associated with pericarditis is often sharp and may worsen with deep breaths or changes in position, providing a distinct clinical presentation that can help differentiate it from other conditions.

In contrast, pleurisy involves inflammation of the pleura, the membranes surrounding the lungs, which causes sharp chest pain during breathing but is not related to the heart. Costochondritis refers to inflammation of the cartilage that connects a rib to the sternum, leading to localized chest discomfort, but it is also not associated with heart inflammation. Myocarditis, while it involves inflammation of the heart muscle itself rather than the pericardial sac, presents with different symptoms, such as fatigue and palpitations, and may not specifically include chest pain as a distinguishing feature. Thus, pericarditis is the condition that accurately matches the description provided in the question.