**Core Concept**
Pulmonary embolism (PE) is a potentially life-threatening condition where one or more pulmonary arteries become blocked by a blood clot, leading to impaired gas exchange and subsequent respiratory distress. In the postoperative period, immobility, venous stasis, and hypercoagulability increase the risk of developing deep vein thrombosis (DVT), which can subsequently embolize to the lungs.

**Why the Correct Answer is Right**
The patient's symptoms of breathlessness and chest pain, coupled with echocardiographic evidence of right ventricular dilatation and tricuspid regurgitation, are highly suggestive of a pulmonary embolism. The right ventricle is particularly vulnerable to the increased pressure and resistance caused by the embolus, leading to its dilatation and subsequent tricuspid regurgitation. This is a classic presentation of a large pulmonary embolism.

**Why Each Wrong Option is Incorrect**
**Option A:** Acute MI typically presents with left ventricular dilatation and signs of left-sided heart failure, rather than right-sided heart failure.
**Option C:** Hypotensive shock can present with a wide range of symptoms, but the specific echocardiographic findings of right ventricular dilatation and tricuspid regurgitation are not typical.
**Option D:** Cardiac tamponade typically presents with signs of left-sided heart failure and a pericardial effusion on echocardiography, rather than right-sided heart failure.

**Clinical Pearl / High-Yield Fact**
In patients who have undergone major surgery, it is essential to be vigilant for signs of pulmonary embolism, as early diagnosis and treatment can significantly improve outcomes. A high index of suspicion, coupled with the use of D-dimer testing and imaging studies (such as CT pulmonary angiography), can help identify patients at risk.

✓ Correct Answer: B. Pulmonary embolism