The current source during ventricular excitation of the in situ heart has not been well characterized. We analyzed current dipoles of ventricular excitation by magnetocardiography (MCG) in 16 healthy subjects and 10 patients with the Wolff-Parkinson-White syndrome or premature ventricular contraction. Single current dipoles were estimated by MCG with the spatial position, direction, and strength in the initial 40 ms of QRS (moving dipole analysis). In 12 of the 16 healthy subjects, the origin of current dipoles moved consecutively from the initial position with the increase in the peak strength at 30 ms of QRS. In the other 4 healthy subjects, dipoles moved discontinuously jumping to the right-anterior thorax at 17.8 ms (mean). In abnormal ventricular excitation, the dipoles remained in the initial position with little movement, smaller strength of dipole than that of normal with a delayed peak time. The moving dipole analysis can be applied to determine spatial distribution of normal and abnormal excitation sources at the initial phase of ventricular depolarization in the in situ heart.