Medical system for mapping of action potential data comprising an elongated medical mapping device suitable for intravascular insertion having an electrode assembly located at a distal portion of the mapping device a data processing and control unit for processing data received from the mapping device, the data processing and control unit including a model generator for visualizing a 3-dimensional heart model based on one of electrical navigation system, MRI or CT 3D scan data of a heart, a display unit for simultaneously displaying both the 3-dimensional heart model visualization and the processed data of the mapping device in form of a model visualization of action potential data, characterized in that the model generator is configured to structure the 3D scan data of the heart into 6 directions a, b, c, d, e and f of a cube, each direction is associated with a separate Cartesian coordinate system with X ( a, b, c, d,e or f), Y ( a,b,c,d,e or f), Z ( a,b,c,d,e or f) coordinates, wherein for assigning each of the 3D scan data point to one of the 6 directions (a, b, c, d, e or f) the following 6 true or false tests are applied: X max a − X mes a > Z mes a ∧ Y max a − Y mes a > Z mes a X max b − X mes b > Z mes b ∧ Y max b − Y mes b > Z mes b X max c − X mes c > Z mes c ∧ Y max c − Y mes c > Z mes c X max d − X mes d > Z mes d ∧ Y max d − Y mes d > Z mes d X max e − X mes e > Z mes e ∧ Y max e − Y mes e > Z mes e X max f − X mes f > Z mes f ∧ Y max f − Y mes f > Z mes f wherein X max, Y max, Z max indicates the maximum leg length of the respective X, Y and Z axis, respectively, of the coordinate system, and wherein X mes, Y mes indicates a projection of a 3D scan data point on the X, Y planes, respectively, and Z mes indicates the distance of the 3D scan data point to the center of the coordinate system, wherein each of the data points is assigned to the direction (a, b, c, d, e or f) for which the test outcome is true. an elongated medical mapping device suitable for intravascular insertion having an electrode assembly located at a distal portion of the mapping device a data processing and control unit for processing data received from the mapping device, the data processing and control unit including a model generator for visualizing a 3-dimensional heart model based on one of electrical navigation system, MRI or CT 3D scan data of a heart, a display unit for simultaneously displaying both the 3-dimensional heart model visualization and the processed data of the mapping device in form of a model visualization of action potential data, characterized in that the model generator is configured to structure the 3D scan data of the heart into 6 directions a, b, c, d, e and f of a cube, each direction is associated with a separate Cartesian coordinate system with X ( a, b, c, d,e or f), Y ( a,b,c,d,e or f), Z ( a,b,c,d,e or f) coordinates, wherein for assigning each of the 3D scan data point to one of the 6 directions (a, b, c, d, e or f) the following 6 true or false tests are applied: X max a − X mes a > Z mes a ∧ Y max a − Y mes a > Z mes a X max b − X mes b > Z mes b ∧ Y max b − Y mes b > Z mes b X max c − X mes c > Z mes c ∧ Y max c − Y mes c > Z mes c X max d − X mes d > Z mes d ∧ Y max d − Y mes d > Z mes d X max e − X mes e > Z mes e ∧ Y max e − Y mes e > Z mes e X max f − X mes f > Z mes f ∧ Y max f − Y mes f > Z mes f wherein X max, Y max, Z max indicates the maximum leg length of the respective X, Y and Z axis, respectively, of the coordinate system, and wherein X mes, Y mes indicates a projection of a 3D scan data point on the X, Y planes, respectively, and Z mes indicates the distance of the 3D scan data point to the center of the coordinate system, wherein each of the data points is assigned to the direction (a, b, c, d, e or f) for which the test outcome is true. wherein X max, Y max, Z max indicates the maximum leg length of the respective X, Y and Z axis, respectively, of the coordinate system, and wherein X mes, Y mes indicates a projection of a 3D scan data point on the X, Y planes, respectively, and Z mes indicates the distance of the 3D scan data point to the center of the coordinate system, wherein each of the data points is assigned to the direction (a, b, c, d, e or f) for which the test outcome is true.