This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
Phosphodiesterase inhibitor used for erectile dysfunction 
Select and explain. 
A. Sildenafil, B. Amrinone, C. Milrinone, D. Tamoxifen
A: Sildenafil
Answer: A: Sildenafil 
Explanation: Ref: KD Tripathi, 7th ed. pg. 303* Sildenafil is an orally active drug for treatment of ED. Sildenafil acts by selectively inhibiting PDE-5, causing increase in cGMP and enhancing Nitric Oxide action on corpus cavernosum.* Amrinone and Milrinone are PDE-3 inhibitor and are also called inodilators. They are used in CHF.* Tamoxifen is a selective estrogen receptor modulator, used in breast cancer.