**Core Concept**
Prinzmetal angina, also known as variant angina, is a type of chest pain characterized by transient, episodic, and reversible myocardial ischemia. This condition is distinct from typical angina, which occurs in response to physical exertion or emotional stress.

**Why the Correct Answer is Right**
Prinzmetal angina is caused by transient, reversible spasm of the coronary arteries, leading to a reduction in blood flow to the heart muscle. This spasm is thought to be due to an imbalance between vasodilating and vasoconstricting substances in the arterial wall, leading to an increase in vascular tone. The spasm can be triggered by a variety of factors, including cold temperatures, emotional stress, and certain medications.

**Why Each Wrong Option is Incorrect**
**Option A:** Angina after extreme exertion is more typical of stable angina, which is caused by atherosclerotic plaque buildup in the coronary arteries, rather than transient spasm.

**Option B:** Atherosclerotic blockade is a characteristic of stable angina, not Prinzmetal angina. Prinzmetal angina is not caused by a blockage of the coronary arteries, but rather by transient spasm.

**Option D:** Calcium channel blockers are actually effective in treating Prinzmetal angina by preventing the transient spasm of the coronary arteries. They work by relaxing the smooth muscle cells in the arterial wall, thereby improving blood flow to the heart muscle.

**Clinical Pearl / High-Yield Fact**
It's essential to differentiate Prinzmetal angina from typical angina, as the treatment approaches differ significantly. Prinzmetal angina is often managed with calcium channel blockers, nitrates, or other vasodilators, whereas typical angina is managed with beta-blockers, nitrates, and lifestyle modifications.

**✓ Correct Answer: C. Caused due to spasm of artery**