Clinical Proof-of-concept Study for the Combination BAY60-4552 / Vardenafil for the Treatment of Erectile Dysfunction Not Sufficiently Responsive to Standard Therapy With PDE5 Inhibitors

Inclusion Criteria: * Open-label run-in phase (first four weeks): * Written informed consent signed before any study-specific procedure * History of ED (Erectile Dysfunction) for at least 6 months prior to screening, defined as "the inability to achieve and maintain an erection of the penis sufficient to complete satisfactory sexual intercourse"; the diagnosis of ED has to be confirmed by a physician * Stable, heterosexual relationship for at least 6 months prior to screening * Aged 18 to 64 years (inclusive) at the first screening examination * History of previous use of at least 1 marketed PDE5 (Phosphodiesterase 5) inhibitor and insufficient therapeutic efficacy despite use of the highest approved dose * Double-blind treatment phase (last four weeks): * At least 4 attempts at sexual intercourse on 4 separate days during the open-label run-in phase with use of 20 mg vardenafil approximately 1 hour before attempting intercourse * IIEF EF (International Index of Erectile Function - Erectile Function subscale) score \<17 * At least 50% of attempts at sexual intercourse during the open-label run-in phase were unsuccessful Exclusion Criteria: * Contraindication to use of vardenafil * History of prostatectomy due to prostate cancer, including nerve-sparing techniques. * Concomitant use of adrenergic blockers * History of spinal cord injury * Resting hypotension, i.e. SBP (Systolic Blood Pressure) \<100 mmHg at rest * Moderate / severe hypertension, i.e. SBP \>170 mmHg or DBP \>110 mmHg at rest * Symptomatic orthostatic hypotension with a decrease in SBP \>20 mmHg or in DBP (Diastolic Blood Pressure) \>10 mmHg subsequent to change from the supine to standing position