There is increasing use of radio frequency (RF) ablation with long electrodes in the intraoperative treatment of atrial fibrillation. Nevertheless, the disparity in the lesion geometry in both depth and width is the major pitfall in the use of RF currents. The objective of this study was to differentiate the shape and size of long lesions created by three surface application electrodes (SAE) and two intramural electrodes (IE). The SAE included a standard multi-polar catheter, and two standard electrosurgical pencils. The IE consisted of a needle and a wire both intramurally buried. The lesions were created on fresh fragments of porcine ventricular tissue. The IE created lesions with a curved prism-like shape around the electrode body, with homogeneous characteristics along the lesion trajectory. On the contrary, the lesions created with the SAE were in the shape of an hourglass. They showed a different geometry between the central zone and the edge zone (p<0.001 for depth and surface width). Electrical impedance evolution was recorded during the RF heating. We observed a slow decrease of the impedance in all the electrodes, except in the wire electrode. In conclusion, the results suggest that the IE might be a more suitable option than SAE when it is necessary to create long and homogeneous thermal lesions.