The purpose of this study was to evaluate cardiopulmonary effects of MLBP-TIVA with or without controlled ventilation in horses and to determine effects of positioning on cardiovascular function in mechanically ventilated horses.Five healthy adult horses were anesthetized with MLBP-TIVA for 2-hours on 3-occasions at 4-week interval with (CMV-group) or without controlled mechanical ventilation(SB-group) and in lateral(LR-group) or dorsal(DR-group) recumbency.Anesthesia was induced with lidocaine(1 mg/kg:Ⅳ) and propofol(3 mg/kg:Ⅳ) following premedications with medetomidine(0.005 mg/kg:Ⅳ) and butorphanol(0.02 mg/kg:IV),and then maintained by propofol infusion combined with constant rate infusions of medetomidine(0.0035 mg/kg/h),lidocaine(3 mg/kg/h) and butorphanol(0.024 mg/kg/h).Data were compared between groups using repeated-measures ANOVA.The level of significance was set at P＜0.05.