Okay, let's tackle this question. The patient is a 20-year-old woman with non-exertional chest pain and multiple non-ejection clicks on auscultation. The question is asking for the investigation of choice.

First, non-ejection clicks are a key clue here. I remember that non-ejection clicks are often associated with mitral valve prolapse (MVP). MVP is a common condition, especially in young women, and can present with chest pain that's not necessarily related to exertion. The non-ejection clicks occur because the mitral valve leaflets snap back during systole, creating that sound.

So, the core concept here is the correlation between auscultatory findings and the underlying cardiac condition. The investigation of choice for MVP would be an echocardiogram. Echocardiography allows visualization of the mitral valve structure, leaflet movement, and any regurgitation. It's non-invasive and provides detailed images of the heart's anatomy.

Now, the incorrect options. Let's think about what other investigations might be considered. An ECG could show nonspecific ST-T changes but wouldn't visualize the valve. A chest X-ray might show a normal or slightly enlarged heart but isn't specific for MVP. Stress testing is used for ischemic heart disease, which is unlikely here. MRI is more detailed but less accessible and more expensive than echo. So, those options are incorrect because they don't directly visualize the mitral valve structure.

The clinical pearl here is that non-ejection clicks in a young woman with chest pain are classic for MVP, and echocardiogram is the gold standard for diagnosis. Students should remember the association between specific auscultatory findings and the appropriate imaging modality.

**Core Concept**
Non-ejection clicks are hallmark auscultatory findings in **mitral valve prolapse (MVP)**, a common cause of non-exertional chest pain in young females. The investigation of choice for confirming MVP and assessing valvular morphology is **echocardiography**.

**Why the Correct Answer is Right**
Echocardiography (transthoracic or transesophageal) directly visualizes mitral valve leaflet prolapse, chordal elongation, and regurgitation. It is non-invasive, widely available, and provides real-time imaging of the mitral apparatus, making it the gold standard for diagnosing MVP. Non-ejection clicks occur due to sudden tensing of the mitral valve apparatus during mid-systole, a feature best confirmed by echocardiographic visualization of leaflet displacement.

**Why Each Wrong Option is Incorrect**
**Option A:** *Electrocardiogram (ECG)* – May show nonspecific ST-T changes but cannot visualize mitral valve structure.
**Option B:** *Chest X-ray* – Might show a "double density" sign (left atrial enlargement) in advanced MVP but lacks specificity.
**Option C:** *Stress test* – Used for ischemic heart disease; irrelevant for MVP.
**Option D:** *Cardiac MRI* – Provides high-resolution imaging but is not first-line due to cost and availability compared to echocardiography.

**Clinical Pearl / High-Yield Fact**
Non-ejection clicks in young women with chest pain are **classic for MVP**. Always prioritize **echocardiography** over other modalities for valvular disorders

✓ Correct Answer: D. Echocardiography