the brain, heart, and  vascular smooth muscle . [9]  It is thought that the inhibition of PDE1 by sildenafil and vardenafil leads to  vasodilation ,  flushing , and  tachycardia . [9]  Tadalafil inhibits PDE11 more than sildenafil or vardenafil. [9]  PDE11 is expressed in  skeletal muscle , the  prostate , the