Abstract: Various methods of treating a heart of a patient having a cardiac arrhythmia are disclosed. The method can comprise dissecting tissue at an inferior aspect of a right inferior pulmonary vein of the patient to create an oblique sinus defect, dissecting tissue to open a space between a superior vena cava and a left atrium, and dissecting tissue to open a space across a transverse sinus between a pulmonary artery and a roof of the left atrium. The method can further comprise passing a catheter through an oblique sinus defect underneath the heart and beyond a left ventricle and passing a first flexible guiding device across the transverse sinus and under the superior vena cava and the pulmonary artery.