This study was conducted to investigate the effect of oxytocin in vivo andin vitro on the heart and to determine its possible mechanisms of actionunder in vitro conditions using the isolated perfused rat heart as anexperimental model. In addition, in the in vivo study the effect of oxytocinon the systolic blood pressure was evaluated.It is composed of the in vitro part which composed of 6 groups :1- Control group, 2- Oxytocin group, 3- L-NAME group, 4- Atropine group, 5- Gadolinium group, 6- Propranolol group. The in vivo part which composed of 2 groups : 1- Control group and 2- In vivo oxytocin group.