The invention relates to a device and to a method for visual assistance during the electrophysiological use of a catheter in the heart, enabling electroanatomic 3D mapping data relating to an area of the heart to be treated to be visualized during the use of the catheter. Before the catheter is used, 3D image data of a body region containing the area to be treated is detected by means of a method for tomographic 3D imaging. The area to be treated or significant parts thereof are extracted from said 3D image data, in order to obtain selected 3D image data. The electroanatomic 3D mapping data and the selected 3D image data obtained are then classed in terms of position and dimension, and are adjacently visualized, for example, during the catheter ablation. The inventive method and associated device enable the orientation of the operator to be improved during the use of a catheter in the heart.