BACKGROUND Catheter ablation of premature ventricular complexes (PVCs) has been used as a curative therapy in many cases. Intracardiac ultrasound with a magnetic sensor probe has recently become available for catheter ablation. In this study, we assessed a new mapping method, contraction mapping, for determining the optimal ablation sites using intracardiac ultrasound and M-mode. This study sought to assess the accuracy of the new mapping method using intracardiac echocardiography. METHODS Eighteen patients (10 males and eight females; mean age, 63±12 years) with 104 mapping points diagnosed as idiopathic PVCs were included in this study. At the mapping points, the time interval from the onset of the QRS to the onset of the contraction (QRS-c-time) and the local activation time were measured using M-mode with an intracardiac echo probe and using the conventional method. The correlation between the QRS-c-time and local activation time were studied. RESULTS The QRS-c-time was significantly correlated with the local activation time (activation time=-66.8+0.882 * QRS-c-time, R2=0.728, p<0.0001). CONCLUSIONS Contraction mapping could help determine the local activation time without the delivery of a catheter to the mapping points.