Objectives: To evaluate the difference of tip position determined by two types of maximal P wave of intracavitary electrocardiography (IC-ECG). Patients and methods: Patients with two major types of maximal P wave were allocated into two groups (P-max and P-alter). Tip positions were recorded on computed tomography (CT) and chest X-ray (CXR). Demographic data, procedure time, catheter length, and final tip position were recorded and analyzed. Results: Two hundred and twenty patients were included, and 203 patients were eligible for final analyses. Maximal P wave may sustain for several centimeters (0-3 cm). Tip position determined by P-alter were mostly in upper atrium (80/102), and tip position determined by P-max were mostly on cavoatrial junction (52/101). Tip may move cephalad with patient’s position changed from supine to upright. Conclusion: Tip positions determined by P-alter were mostly in upper atrium, however both criteria are acceptable for tip positioning. Post operative imaging for tip position would better use CT. CXR may underscore catheter position determined by IC-ECG.