**Core Concept**
Buerger's disease, also known as thromboangiitis obliterans, is a rare, non-atherosclerotic, segmental inflammatory disease affecting the small and medium-sized arteries and veins of the limbs. It is characterized by inflammation, thrombosis, and eventually, ischemia of the affected tissues.

**Why the Correct Answer is Right**
The most common cause of death in patients with Buerger's disease is myocardial infarction. This is due to the diffuse nature of the disease, which can affect not only the limbs but also other vascular beds, including the coronary arteries. The inflammation and thrombosis associated with Buerger's disease can lead to the formation of atherosclerotic plaques in the coronary arteries, increasing the risk of myocardial infarction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while Buerger's disease can cause limb ischemia, it is not the most common cause of death in patients with this disease.
**Option B:** This option is incorrect because while smoking is a major risk factor for Buerger's disease, it is not a direct cause of death in patients with this disease.
**Option C:** This option is incorrect because while cardiac complications can occur in patients with Buerger's disease, they are not the most common cause of death.

**Clinical Pearl / High-Yield Fact**
Patients with Buerger's disease are at increased risk of developing atherosclerotic plaques in other vascular beds, including the coronary arteries, due to the diffuse nature of the disease. This highlights the importance of aggressive risk factor modification and monitoring for cardiac complications in patients with this disease.

**Correct Answer:** D. Myocardial infarction.