**Core Concept**
Acute rheumatic fever (ARF) is a complication of Streptococcus pyogenes infection, leading to inflammation and damage in various tissues. The disease is characterized by carditis, arthritis, chorea, and other systemic manifestations.

**Why the Correct Answer is Right**
In ARF, the autoimmune response triggered by the streptococcal infection leads to the deposition of immune complexes and activation of complement. This results in the inflammation of the heart valves, particularly the mitral valve, which is a hallmark of rheumatic carditis. The inflammation can also affect other tissues, such as the joints, skin, and nervous system. The Aschoff bodies, a characteristic pathological feature of rheumatic carditis, are collections of immune cells and fibrin that form in the heart tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** Libman-Sacks endocarditis is a feature of systemic lupus erythematosus (SLE), not ARF. It is characterized by the deposition of immune complexes on the heart valves.
**Option B:** Granulomatous inflammation is more characteristic of sarcoidosis, a different condition that affects various organs, including the lungs, skin, and lymph nodes.
**Option C:** Rheumatic nodules are a feature of ARF, representing areas of granulomatous inflammation in the skin, particularly on the elbows and knees.

**Clinical Pearl / High-Yield Fact**
ARF is a preventable cause of heart disease in children, and prompt treatment with penicillin can prevent the development of rheumatic carditis.

**Correct Answer: C.**