Which condition is characterized by inflammation of the myocardium?

Myocarditis is characterized specifically by the inflammation of the myocardium, which is the muscular layer of the heart responsible for contraction and pumping blood. This condition can be caused by a variety of factors, including viral infections, autoimmune diseases, and exposure to certain toxins. The inflammation can disrupt the normal electrical and mechanical functions of the heart, leading to various symptoms such as chest pain, fatigue, and heart palpitations.

Understanding the distinction among the other choices provided helps clarify why myocarditis is the correct answer. Endocarditis refers to the inflammation of the inner lining of the heart chambers and valves, which is distinct from inflammation of the muscular layer. Acute pericarditis involves inflammation of the pericardium, the fibrous sac surrounding the heart, and similar to chronic pericarditis, it affects a different structure entirely. Hence, myocarditis specifically addresses the inflammation of the heart muscle, making it the correct option in this context.