Study For Which Treatment, Tadalafil or Sildenafil, is Preferred For Problems Getting or Maintaining an Erection

A Multicenter Open-Label Study to Determine Treatment Preference of Tadalafil (IC351, LY450190) or Sildenafil Citrate in the Oral Treatment of Erectile Dysfunction

To determine if men prefer tadalafil or sildenafil for getting and keeping an erection after treatment with both drugs.

Inclusion Criteria:

• History of erection problems
• Never taken treatments known as PDE5 inhibitors for erection issues
• Abstain from using any other erection treatments during the study
• Anticipate a monogamous female sexual relationship
• Must be able to make required sexual intercourse attempts

Exclusion Criteria:

• History of other primary sexual disorder
• Treatment with nitrates
• Have a penile implant or clinically significant penile deformity
• History of certain heart problems
• Do not meet certain lab value reference ranges