Intracardiac echocardiography (ICE) serves as an adjunct to fluoroscopy for electrophysiological procedures by identifying critical anatomic landmarks and confirming catheter-endocardial contact. In the present study, we investigated the usefulness of ICE for radiofrequency catheter ablation. ICE was utilized to guide transseptal puncture in 19 patients undergoing radiofrequency catheter ablation. The fossa ovalis, which was one critical anatomic landmark, had an average vertical diameter of 18.5 ± 6.9 mm and an average horizontal diameter of 10.0 ± 2.4 mm, as measured by ICE and fluoroscopy. Although there was only a small shift of the puncture site in the horizontal direction, the puncture site shifted towards the upper edge of the fossa ovalis for 17 patients (89%). Furthermore, we could verify that the distance between the apex of the tent-shape formed by the pressure of the puncture needle in the fossa ovalis and the left atrial wall opposing it was sufficient to carry out the procedure safely. Confirming the puncture site using ICE is useful in carrying out transseptal left heart catheterization safely.