Purpose: To examine the efficacy of an alpha-1 blocker and its correlation to structural alteration of the prostatic urethra and the loss of energy in the urine flow using a virtual urethra processed from an endoscopic video image. Materials and Methods: Video images of the prostatic urethra were recorded during cystourethroscopy in 11 patients with benign prostatic hyperplasia (BPH) before and after treatment with an alpha-1 blocker, naftopidil. The three-dimensional (3D) structure of the prostatic urethra was reproduced from video files. Fluid dynamic analysis and hydraulic energy calculations were performed using the "virtual" 3D urethral images. Results: In 9 of 11 patients studied, an 11% improvement in the loss of energy (range, 1%-82%) was seen. Alpha-1 blocker treatment mediated the disappearance or decrease of the bulky vortex formation in seven patients, which led to an improved urinary stream. A positive correlation was found between improved energy loss and residual urine volume (P=0.0312). Conclusion: Alpha-1 blocker therapy led to a decreased energy loss in the urine flow in the prostatic urethra in relation to the improvement of clinical symptoms. The cystourethroscopy could be a tool to assess the urethral resistance in patients with BPH using image processing methodology.