**Core Concept**
Acute rheumatic fever (ARF) is a complication of untreated or inadequately treated group A beta-hemolytic streptococcal (GABHS) pharyngitis. The disease process involves an autoimmune response to the streptococcal infection, leading to inflammation and damage to various tissues, particularly the heart.

**Why the Correct Answer is Right**
The Aschoff body is a characteristic pathological finding in ARF, representing a granulomatous lesion composed of an aggregation of immune cells, including macrophages, lymphocytes, and plasma cells. These lesions are typically found in the heart, particularly in the endocardium and myocardium. The Aschoff body is a result of the autoimmune response to the streptococcal infection, leading to inflammation and tissue damage.

**Why Each Wrong Option is Incorrect**
**Option A:** Aschoff bodies can be expected at autopsy in a case of acute rheumatic fever, so this is incorrect.
**Option B:** Rheumatic heart disease, characterized by valvular damage, is a common complication of ARF, making this option incorrect.
**Option C:** Fibrinous pericarditis, an inflammation of the pericardium, is another potential finding in ARF, so this is incorrect.

**Clinical Pearl / High-Yield Fact**
Mnemonic to remember the Jones criteria for diagnosing acute rheumatic fever: "Major criteria" include carditis, polyarthritis, chorea, erythema marginatum, and subcutaneous nodules, while "Minor criteria" include fever, arthralgia, and laboratory evidence of recent streptococcal infection.

**Correct Answer: D.**