To elucidate the role of PDE5 inhibition in the vicious circle of inflammation and coagulation in neonatal hyperoxic lung disease, we investigated the effect of sildenafil, a selective PDE5 inhibitor [18], using two different treatment strategies: a prophylactic strategy in a lethal model and a more clinically relevant strategy in which treatment was started after injury was induced in a non-lethal lung injury-recovery model. This evidence concerns the gene PDE5A and lung disorder.