This study was conducted to determine whether mirodenafil 100 mg, when administered on demand to patients with benign prostatic hyperplasia (BPH) who are receiving α1-blocker therapy, is safe with regard to the cardiovascular system and whether it improves lower urinary tract symptoms (LUTS) and sexual function. The study involved 121 LUTS/BPH patients who had been treated for at least 3 months with α1-blockers before being administered with mirodenafil 100 mg on demand. Before the start of mirodenafil administration, the blood pressure, heart rate, international prostate symptom score (IPSS)/quality of life (QoL), peak urine flow rate (Qmax), post-voiding residual urine volume (PVR), and international index of erectile function-5 (IIEF-5) of each patient were measured. At 4 and 8 weeks after commencing mirodenafil administration, the blood pressure and heart rate were measured again, any adverse effects of mirodenafil were assessed, and sexual function and voiding symptoms were re-evaluated. Of the 121 patients, 73 (60.3%) completed the 8-week clinical trial. Significant changes in blood pressure and heart rate were not observed during the study. Significant improvements in the IIEF-5 and the IPSS/QoL, but not the Qmax or PVR, were observed. The results of this study suggest that the administration of mirodenafil 100 mg on demand may induce few hypotensive interactions and may be acceptably effective with regard to improving LUTS and sexual function.