A catheter apparatus is provided for use in the treatment of heart arrhythmia having a catheter shaft, a mapping and ablation catheter disposed within the shaft, and a control mechanism coupled to both the shaft and catheter. The catheter shaft includes a main body and a coaxial tip section joined to the main body. The tip section can be rotated about a central axis and curved away from the central axis in a controlled manner. The mapping and ablation catheter can be extended outward from the catheter shaft where it is able to take the form of a pre-stressed curve. The control mechanism controls axial rotation of the tip section, the degree of deflection of the tip section and longitudinal movement of the mapping and ablation catheter with respect to the catheter shaft. Preferably, the mapping and ablation catheter forms a pre-stressed loop when it is fully extended from the catheter shaft. In another aspect of this invention, it provides a method for treatment of a heart arrhythmia having the steps of (1) obtaining cardiac image data from a medical imaging system, (2) creating a 3D model from this cardiac image data, (3) registering the 3D model to an interventional system, (4) positioning a catheter apparatus within a chamber of the heart, (5) displaying the catheter apparatus over the registered 3D model on the interventional system, (6) navigating the catheter apparatus within the heart guided by the registered 3D model, and (7) having the catheter apparatus ablate heart tissue at select locations.