In the RAAS, sildenafil has shown to enhance circulating ACE2 concentration and to exert dual effects on the angiotensin II-AT1-angiotensin 1–7-AT2 balance, with uncertain effects on COVID-19 [367], while sildenafil may provide protective effects for acute lung injuries due to its abilities to inhibit neutrophilic actions within the lungs and release of pro-inflammatory cytokines, reduce oxidative stress, inhibit apoptosis of epithelial cells, prevent lung edema formation, and improve respiratory parameters [368–370]. The gene discussed is ACE2; the disease is COVID-19.