Background Cardiac MRI features are not well-defined in immune checkpoint inhibitor (ICI)-induced myocarditis (ICI-M), a severe complication of ICI therapy in patients with cancer. Purpose To analyze the cardiac MRI features of ICI-M and to explore their prognostic value in major adverse cardiovascular events (MACE). Materials and Methods In this retrospective study from May 2017 to January 2020, cardiac MRI findings (including late gadolinium enhancement [LGE], T1 and T2 mapping, and extracellular volume fraction [ECV] z scores) of patients with ICI-M were compared with those of patients with cancer scheduled to receive ICI therapy (pre-ICI group) and patients with viral myocarditis. As a secondary objective, the potential value of cardiac MRI for predicting MACE in patients with ICI-M by using Cox proportional hazards models was explored. Results Thirty-three patients with ICI-M (mean age ± standard deviation, 68 years ± 14; 23 men) were compared with 21 patients scheduled to receive to ICI therapy (mean age, 65 years ± 14; 14 men) and 85 patients with viral myocarditis (mean age, 32 years ± 13; 67 men). Compared with the pre-ICI group, patients with ICI-M showed higher global native T1, ECV, and T2 z scores (0.03 ± 0.85 vs 1.79 ± 1.93 [P < .001]; 1.34 ± 0.57 vs 2.59 ± 1.97 [P = .03]; and -0.76 ± 1.41 vs 0.88 ± 1.96 [P = .002], respectively), and LGE was more frequently observed (27 of 33 patients [82%] vs two of 21 [10%]; P < .001). LGE was less frequent in patients with ICI-M than those with viral myocarditis (27 of 33 patients [82%] vs 85 of 85 [100%]; P < .001) but was more likely to involve the septal segments (16 of 33 patients [48%] vs 25 of 85 [29%]; P < .001) and midwall layer (11 of 33 patients [33%] vs two of 85 [2%]; P < .001). Septal LGE was the only cardiac MRI predictor of MACE at 1 year even after adjustment for peak troponin (adjusted hazard ratio, 2.7 [95% CI: 1.1, 6.7]; P = .03). Conclusion Cardiac MRI features of immune checkpoint inhibitor (ICI)-induced myocarditis (ICI-M) seem to differ from those in patients scheduled to receive ICIs and patients with viral myocarditis. Septal late gadolinium enhancement might be a predictor of major cardiovascular events in patients with ICI-M. Clinical trial registration no. NCT03313544 © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Edelman and Pursnani in this issue.