Echo Planar Imaging (EPI) is associated with inaccurate velocity quantitation in 4D flow MRI. The systematic errors depend on the orientation of readout and blip phase encoding gradient with respect to the flow direction. This study evaluates EPI-related errors in flow rate and velocity quantitation for in vivo intracardiac 4D flow MRI in a phantom and in ten healthy volunteers. Errors in median flow rate and velocity remain below 10% for normal in vivo intracardiac flow with EPI factor 5. The error is smallest when readout and blip phase encoding gradients are both perpendicular to the main flow.