Atrial fibrillation (AF) is the most common sustained arrhythmia in the western world. Pulmonary vein isolation (PVI) using radiofrequency ablation (RFA) is frequently conducted to treat AF. However, current PVI procedures for lesion formation are guided only with indirect information, which may lead to non-transmural lesions, and contribute to the high recurrence of AF. Therefore, direct lesion quality feedback may potentially improve PVI efficacy. To study the real-time direct guidance capability of polarization sensitive optical coherence tomography (PSOCT), a custom-designed integrated PSOCT-RFA catheter was prototyped and tested in RFA procedures in the left atria of living swine.