What is the difference between endocarditis, myocarditis, and pericarditis?

Depends on which: Itis is a suffix indicating inflammation . If the pericardium , the sack around the heart is inflamed then it called pericarditis . If it's the muscle itself it's called myocarditis . If the valves are damaged and inflamed then it's endocarditis.

Different structures: Endocarditis refers to an infection of the heart valves. Myocarditis is inflammation/infection of the heart muscle. Pericarditis is inflammation the pericardium which is the sac surrounding the heart.