Mechanism cGMP phosphodiesterase inhibitor results in less cGMP degradation and ↑ cGMP Drives smooth muscle relaxation in the corpus cavernosum ↑ blood flow to penis Indications Erectile dysfunction Pulmonary hypertension Toxicity Side effects headache flushing dyspepsia impaired blue-green color vision Do not co-administer with nitrates risk of life-threatening hypotension