This paper describes a study of assessing the effect of reorientation variation on the myocardial blood flow (MBF) estimation from dynamic PET cardiac acquisition using 13NH3. 58 13NH3 dynamic datasets were reoriented with an automatic algorithm. For each dataset a series of 20 random reorientations were generated from the automatically computed result. The variation of MBF with the reorientation parameters was assessed using the coefficient of variation (CV). The mean, standard deviation and max of CV for the 58 datasets with reorientation and center perturbation are computed for the three AHA vessel regions: LAD (4.8%, 3.3%, 21.1%), LCX (4.5%, 3.3%, 20.3%), RCA (5.6%, 5.4%, 30.6%), all regions combined (4.5%, 3.3%, 17.1%). The results show manual adjustment of the reorientation is not expected to cause large variation on the MBF estimation on the three vessel regions or globally, if the placement of the BIF ROI is appropriate.