A method and a device for visually assisting a catheter application on the heart of a patient using an image of the patient obtained by a C-arm X-ray device and using electroanatomical mapping data of the patient obtained by an electromagnetic position detection system and mapping system. The C-arm X-ray device and the electromagnetic position detection system and mapping system are calibrated in relation to each other, by determining a co-ordinate transformation between a co-ordinate system assigned to the C-arm x-ray device and/or a co-ordinate system assigned to the image generated by the C-arm X-ray device and a co-ordinate system assigned to the electromagnetic position detection system and mapping system. The position of the patient is determined during the detection of the image and/or during the detection of the electroanatomic mapping-data and is at least indirectly assigned to the image and/or the electroanatomic mapping-data.