To Determine How Different Doses of Tadalafil Work on Getting and Keeping an Erection 26 or 36 Hours After Taking

A Randomized, Double-Blind, Parallel, Placebo-Controlled Study in Men With Erectile Dysfunction to Evaluate the Efficacy and Safety of Tadalafil When Sexual Attempts Occur at Specific Time Points After Dosing

Study to see how effective different doses of tadalafil are for getting and keeping an erection when sex is attempted after a certain number of hours.

Inclusion Criteria:

• At least 3 months history of erectile dysfunction (ED)
• Anticipate a monogamous relationship with a female sexual partner
• Be able to make minimum required sexual intercourse attempts
• Abstain from using any other ED treatment

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