Electrophysiology (EP) catheters are shown in right anterior oblique view. The surface ECG electrodes are marked with yellow arrows. The decapolar catheter is situated in the coronary sinus and has been introduced from above using a jugular vein puncture. The quadripolar catheter placed anteriorly and pointed downwards is in the right ventricle. Another quadripolar catheter is placed with its tip recording the His bundle potential. Above it an ablation catheter which is also quadripolar can be seen. Ablation catheter can be identified by the larger size of the distal electrode which is used to deliver radiofrequency energy during catheter ablation. The surface ECG electrodes are marked by yellow arrows.