Left ventricular outflow obstruction, rare syndrome of multiple system atrophy manifesting as severely impaired autonomic control of blood pressure. Serious CV events. Angulation, cavernosal fibrosis or Peyronie's disease, priapism. Concomitant w/ other drugs for erectile dysfunction, ritonavir, α-blocker, Na nitroprusside. Bleeding disorder or active peptic ulceration. Galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption. May affect ability to drive or operate machinery. Not indicated in women. Childn <18 yr.