Clinical effectiveness is of the finest tools to evaluate treatment success and is combined of 3 elements: treatment effectivity, side effect profile and patient compliance. Since the 3 main PDE5i's differ in their molecular structure, therapeutic profile and pharmacokinetics, it seems logical to assume that combining 2 different PDE5i's at lower dosage each may be beneficial in comparison to a single PDE5i maximal dose therapy. The aim of this study is to compare the clinical effectiveness of combination therapy (2 lower-dose PDE5i's) versus single maximal dose PDE5i therapy.

This will be a prospective, randomized, 3-arm parallel trial on 60 males with erectile dysfunction (ED) that have never been exposed to PDE5i therapy (naïve patients) will be enrolled. In each group, every patient will receive three treatment regimes (Viagra®50mg & Cialis®10mg, Viagra®100mg, Cialis®20mg), in different sequences of administration.

Inclusion Criteria:

• Age ranging between 35-75 years.
• Sexually active
• IIEF ED domain score 22 and below

Exclusion Criteria:

• Subjects with premature ejaculation as their main sexual complaint.
• Subjects with severe cardiovascular disease
• Subjects with Contraindications to PDE5i therapy. Namely patients receiving treatment with nitrate based medication or patients that for various reasons cannot take PDE5 inhibitors (i.e severe coronary disease, liver or renal failure, concomitant medications, etc.).