ALDH7A1 and angina pectoris: However, the success of sildenafil (Viagra), the first oral PDE5 inhibitor initially developed to treat angina and then approved by the Food and Drug Administration (FDA) for the treatment of male erectile dysfunction, combined with an increasing understanding of PDE biology, has raised new hopes that manipulating PDE activity with greater specificity can yield therapeutic benefits in many diseases (FIGURE 11) (501).