Safety, tolerability, pharmacokinetics and pharmacodynamics will be investigated in this multiple dose escalation study. In three treatments groups different dosages of BAY 60-4552 and vardenafil will be given with patients with erectile dysfunction.

Inclusion Criteria:

• The informed consent must be signed before any study specific tests or procedures are done
• Male patients with a history of erectile dysfunction (ED) for at least 6 months, defined as "the inability to achieve and maintain an erection of the penis sufficient to complete satisfactory sexual intercourse" by the NIH consensus report 1993. The diagnosis of 'Erectile dysfunction' has to be confirmed by a physician
• Age: 18 to 70 years (inclusive) at the first screening examination
• Ethnicity: White
• Body mass index (BMI): equal to or above 18 and below 32 kg / m²
• Confirmation of the patient's health insurance coverage prior to the first screening examination / visit
• Ability to understand and follow study-related instructions

Exclusion Criteria:

• Incompletely cured pre-existing diseases for which it can be assumed that the absorption, distribution, metabolism, elimination and effects of the study drugs will not be normal
• Known hypersensitivity to the study drugs (active substances or excipients of the preparations)
• Known severe allergies, non-allergic drug reactions, or multiple drug allergies
• Any underlying cardiovascular condition, including unstable angina pectoris that would preclude sexual activity according to the NIH consensus report 1993
• History of myocardial infarction, stroke or life-threatening arrhythmia within 6 months prior to screening
• Bleeding disorder
• History of prostatectomy because of prostate cancer, including nerve-sparing techniques. Clarification: Any surgical procedures for the treatment of Benign Prostate Hypertrophy (BPH) are permitted, with the exception of cryosurgery, cryotherapy or cryoablation
• Hereditary degenerative retinal disorders such as retinitis pigmentosa
• History of loss of vision because of NAION (Bayer Study 12912), temporary or permanent loss of vision, including unilateral loss of vision
• History of uni- or bilateral hearing loss