**Core Concept**
Aschoff's nodules are characteristic pathological lesions found in the heart, particularly in the myocardium, associated with rheumatic fever. They are a result of an autoimmune response to Group A beta-hemolytic streptococcal infection.

**Why the Correct Answer is Right**
Aschoff's nodules are granulomatous lesions composed of an aggregation of immune cells, including macrophages, lymphocytes, and plasma cells. They are a hallmark of rheumatic heart disease, which occurs when the immune system mistakenly attacks the heart tissue in response to a streptococcal infection. The lesions are characterized by the presence of Anitschkow cells, which are macrophages with characteristic folded nuclei.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Aschoff's nodules are not associated with sarcoidosis, a condition characterized by the formation of non-caseating granulomas in various organs, including the lungs and lymph nodes.
**Option B:** This option is incorrect because rheumatic heart disease, associated with Aschoff's nodules, is not the same as hypertrophic cardiomyopathy, a condition characterized by thickening of the heart muscle.
**Option C:** This option is incorrect because Aschoff's nodules are not a feature of Kawasaki disease, a condition characterized by inflammation of blood vessels and cardiac complications.

**Clinical Pearl / High-Yield Fact**
Aschoff's nodules are a classic example of an autoimmune response gone awry, highlighting the importance of distinguishing between infectious and autoimmune processes in the differential diagnosis of cardiac lesions.

**Correct Answer:** D. Rheumatic heart disease.