The magnetohydrodynamic (MHD) effect was investigated in the electrocardiogram (ECG) during MRI. ECGs were obtained for 10 healthy subjects inside and outside a 3.0T MRI scanner. The MHD effect was characterized as the difference in voltage between the mean beat from the ECG taken inside the magnet and the one taken outside the magnet. A significant deflection was observed and was found to primarily correspond to the flow of blood in the aortic arch. When subjects were in supine position, the mean amplitude of this deflection was 0.19 ± 0.04 mV, and its mean duration was 0.34 ± 0.02 secs; when in prone position, the mean amplitude of this deflection was 0.21 ± 0.08 mV, and its mean duration was 0.33 ± 0.02 secs. An axial orientation 2D phase contrast MRI scan was performed to allow blood flow and velocity measurements. By characterizing the MHD signal, we can obtain flow information and can develop improved subtraction techniques for ECG during MRI.