Magnetocardiography is the recording of magnetic field (MF) generated by cardiac electrophysiological activity. Being a contactless method, magnetocardiography is ideal for non-invasive cardiac mapping of small experimental animals. The aim of this study was to assess age-related changes of cardiac intervals and of ventricular repolarization (VR) maps in intact rats, by means of magnetocardiographic (MCG) mapping. 24 adult Wistar rats (12 males and 12 females) were investigated, under anesthesia, with the same unshielded 36-channel MCG instrumentation used for clinical recordings. Two sets of measurements were performed from each animal: 1) at the age of 5 months [weight: 297.5 ± 21 gr]; 2) at the age of 14 months [weight: 516.8 ± 180 gr]. RR, PR, QRS, QT_peak, QT_end, JT_peak, JT_end and T_peak-end intervals were measured from MCG waveforms. MCG imaging was automatically obtained as MF maps and as inverse localization of cardiac sources with the Equivalent Current Dipole and Effective Magnetic Dipole models. After averaging 300 seconds of continuous recording, the signal-to-noise ratio was adequate to study atrial and ventricular MF maps and for three-dimensional localization of the underlying cardiac sources. Clear-cut age-related differences in VR duration were evidenced by significantly longer QT_end, JT_end, and T_peak-end intervals in older WRs. As compared to ECG recordings, MCG methodology simplifies reproducible multi-site non-invasive cardiac mapping of anaesthetized rats. In addition MCG mapping provides new information based on quantitative analysis of MF and equivalent sources. In this study statistically significant age-dependent variations of VR intervals were found.