**Core Concept**
Pulmonary hypertension (PH) is characterized by elevated pulmonary vascular resistance due to vascular remodeling and vasoconstriction. Treatment focuses on vasodilators that reduce pulmonary pressure, improve right ventricular function, and prevent further vascular remodeling.

**Why the Correct Answer is Right**
Alpha blockers (e.g., prazosin) are not used in pulmonary hypertension because they primarily cause systemic vasodilation and reflex tachycardia, with minimal effect on pulmonary vasculature. In contrast, calcium channel blockers (A), endothelin receptor antagonists (B), and prostacyclin analogs (D) are well-established therapies that directly relax pulmonary vascular smooth muscle or inhibit vasoconstrictive pathways. Prostacyclin analogs (like epoprostenol) are first-line in severe PH, while endothelin antagonists (e.g., bosentan) block potent vasoconstrictors.

**Why Each Wrong Option is Incorrect**
Option A: Calcium channel blockers (e.g., diltiazem) are used in pulmonary hypertension, especially in pulmonary arterial hypertension (PAH), to reduce pulmonary vascular resistance by blocking L-type calcium channels in pulmonary arteries.
Option B: Endothelin receptor antagonists (e.g., bosentan) block endothelin-1, a powerful vasoconstrictor in PAH, reducing pulmonary vascular resistance.
Option D: Prostacyclin analogs (e.g., iloprost) are potent vasodilators and antiplatelet agents used in PAH, especially in severe cases.

**Clinical Pearl / High-Yield Fact**
Never use alpha blockers in pulmonary hypertension — they can worsen hemodynamics due to reflex sympathetic activation and lack of pulmonary specificity. Always prefer vasodilators with proven pulmonary action.

✓ Correct Answer: C. Alpha blocker