The purpose of this study was to evaluate effects of controlled ventilation and positioning on cardiopulmonary function in horses anesthetized with total intravenous anesthesia using a drug combination of medetomidine,lidocaine,butorphanol and propofol(MLBP-TIVA).Five healthy adult horses were anesthetized with MLBP-TIVA for 2-hours on 3-occasions at 4-week interval.In each occasion,horses were anesthetized in lateral recumbency with(CV-LR-group) or without controlled ventilation(SB-LR-group) or in dorsal recumbency with controlled ventilation(CV-DR-group).