Introduction: Particle beams, such as protons, offer unique radiophysical properties that potentially can be used for catheter-free image-guided ablation of ventricular tachycardia (VT). Biophysiological effects on cardiac tissue and the exact time course of tissue changes remain unclear. This study was conducted to investigate lesions created in left ventricular (LV) myocardium by scanned proton beams using time-course MRI for lesion assessment. Method: Five normal pigs underwent LV ablation using a single dose of 40Gy. ECG-gated CT scans were acquired and three targets in LV myocardium (in anterior wall, posterior wall and apex) were contoured, estimating contractile target motion. After irradiation, contrast (gadolinium)-enhanced cardiac MRI was obtained every 4 weeks. After a follow-up duration of more than 12 weeks, gross and microscopic pathologic investigations were performed. Results: In total, 15 targets were irradiated. Two of the 15 lesions could be detected with MRI at 4 weeks after irradiation and 11 lesions at 8 weeks. At 12 weeks, all lesions were identified on MRI. Figure A shows a representative case of lesion tracking by MRI and gross pathology outcome. Mean lesion volume on time course MRI at 4, 8, 12 and 16weeks were 0.1±0.2cc, 1.6±1.9cc, 4.1±3.3cc and 4.7±3.6cc, respectively. Figure B shows individual lesion volume tracking and mean lesion volume on time course MRI during the follow-up. In the majority of lesions, lesion size plateaued between 12 and 16 weeks. Conclusion: Scanned proton beams could be used for induction of circumscribed LV lesions that were tracked during follow-up by late-gadolinium enhancement.