**Core Concept**
Rheumatic fever is a post-streptococcal autoimmune disease affecting the heart, joints, skin, and brain. It follows untreated or inadequately treated group A streptococcal pharyngitis and manifests with carditis, polyarthritis, chorea, subcutaneous nodules, and erythema marginatum. Key electrocardiographic (ECG) findings include PR interval prolongation and ST segment changes, reflecting myocardial inflammation.

**Why the Correct Answer is Right**
Cardiomegaly is not a classic or specific feature of rheumatic fever. While cardiac involvement occurs, it is typically due to valvular damage (e.g., mitral regurgitation), not true cardiomegaly. ECG changes such as **increased PR interval** (due to conduction system inflammation) and **ST segment elevation** (in early myocarditis) are hallmark findings. Joint pains (polyarthritis) are common, and these features are part of the Jones criteria. Cardiomegaly is not a primary clinical sign and may be absent or secondary to chronic heart failure.

**Why Each Wrong Option is Incorrect**
Option B: Joint pains are a hallmark of polyarthritis in rheumatic fever, often affecting large joints symmetrically.
Option C: ST segment elevation is seen in early myocardial inflammation, especially in the context of acute carditis.
Option D: Increased PR interval reflects conduction system involvement, a key ECG feature of rheumatic fever.

**Clinical Pearl / High-Yield Fact**
Remember: **"PR interval prolongation and ST segment changes"** are ECG signs of rheumatic fever, while **cardiomegaly is not a primary feature**—it may appear only in chronic or advanced stages due to heart failure, not acute disease.

✓ Correct Answer: A. Cardiomegaly