TY - JOUR AU - Montorsi, F; Hellstrom, W J; Valiquette, L North American and European Vardenafil Groups TI - Vardenafil provides reliable efficacy over time in men with erectile dysfunction JO - Urology VL - 64 PY - 2004 DO - 10.1016/j.urology.2004.07.032 SP - 1187 EP - 1195 N1 - et al. ER -