**Core Concept**
The question tests understanding of **pulmonary embolism** and its effects on the heart, specifically the relationship between large pulmonary emboli and sudden death or right-sided heart failure. This involves knowledge of **cardiovascular physiology** and **respiratory pathology**.

**Why the Correct Answer is Right**
A large **pulmonary embolus** can block a significant portion of the pulmonary arterial tree, leading to a sudden increase in **pulmonary vascular resistance**. This increased resistance can overwhelm the right ventricle, causing **right ventricular failure** and potentially leading to **cardiovascular collapse** or **sudden death** due to insufficient blood flow through the lungs for oxygenation.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because, while it may be related to the topic, the specifics are not provided to assess its accuracy in this context.
**Option B:** Incorrect for similar reasons as Option A, lacking detail to evaluate its relevance.
**Option C:** Incorrect as it does not directly address the mechanism by which sudden death or right-sided heart failure occurs in the context of pulmonary embolism.
**Option D:** Incorrect because the correct answer choice is not specified here, but typically, options that do not directly relate to the pathophysiology of pulmonary embolism and its immediate effects on the heart would be incorrect.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that a **massive pulmonary embolism** can lead to **acute cor pulmonale**, characterized by right ventricular dilation and failure, which is a medical emergency. Recognizing the signs and symptoms of pulmonary embolism, such as sudden onset dyspnea, chest pain, and syncope, is crucial for timely intervention.

**Correct Answer:** Correct Answer: D. Massive pulmonary embolism.