**Core Concept**
Left atrial Myxoma is a type of cardiac tumor that arises from the left atrium, most commonly near the fossa ovalis. These tumors can be benign or malignant, but most are benign. Myxomas are often associated with various systemic symptoms due to embolization, inflammation, and other mechanisms.

**Why the Correct Answer is Right**
The correct answer, **C. Markedly enlarged left atrium**, is incorrect because left atrial Myxoma typically presents as a solitary, mobile mass within the left atrium, rather than causing significant enlargement of the left atrium. While left atrial enlargement can occur due to chronic left-sided heart failure or other causes, it is not a characteristic feature of left atrial Myxoma.

**Why Each Wrong Option is Incorrect**
**Option A:** Raised ESR (Erythrocyte Sedimentation Rate) is indeed a common feature of left atrial Myxoma, as the tumor can cause chronic inflammation and production of inflammatory cytokines.
**Option B:** Pyrexia (fever) is also a possible symptom of left atrial Myxoma, likely due to the chronic inflammatory response and potential embolization of tumor fragments.
**Option D:** Systemic Embolism is a well-known complication of left atrial Myxoma, as fragments of the tumor can break off and travel to distant sites, causing embolic events.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that left atrial Myxoma can mimic other cardiac conditions, such as mitral stenosis or atrial fibrillation, due to its location and potential for embolization. A high index of suspicion and careful clinical evaluation are necessary for accurate diagnosis.

**✓ Correct Answer: C. Markedly enlarged left atrium**