In presence of a high magnetic field, the blood flow in the aorta induces an electrical potential which is responsible for an increase of the T -wave in the electrocardiogram (ECG). This phenomenon may perturb ECG-gated imaging. The aim of this numerical study is to reproduce this experimental observation through computer simulations. The proposed model consists of three components: magnetohydrodynamics (MHD) in the aorta, bidomain equations in the heart and electrical diffusion in the rest of the body. These models are strongly coupled together and solved with finite elements. Some numerical results without and with a magnetic field are presented and discussed. When the magnetic field increases from B = 0 T to B = 3 T , it is observed numerically that the potential in the lead I of the ECG doubles during the T -wave, reaching the level of the QRS peak. All numerical computations were performed on a realistic "averaged" human model