BACKGROUND: Acute myocarditis (AM) is induced by multiple factors, and its clinical symptoms and prognosis vary significantly. Existing diagnostic and prognostic assessment methods have certain limitations. Myocardial strain analysis based on cardiac magnetic resonance feature tracking (CMR-FT) can detect myocardial damage in the subclinical stage, but studies on the correlation between left atrial (LA) strain and the prognosis of AM are relatively limited. This study aimed to assess whether impaired LA strain parameters based on CMR-FT-derived techniques can be used to predict AM outcomes. METHODS: A retrospective cohort study was conducted on the clinical and functional parameters, including LA strain, of 91 patients diagnosed with AM between September 2020 and June 2022. The patients were stratified into the following two groups according to the presence or absence of major adverse cardiovascular events (MACEs): the MACE group, and the non-MACE group. The MACEs identified in our study were: (I) cardiovascular death; (II) hospital admission for heart failure; (III) severe arrhythmia (frequent ventricular extrasystole, ventricular tachycardia, or ventricular fibrillation); and (IV) dilated cardiomyopathy (DCM). The receiver operating characteristic (ROC) curve was used to define a threshold value for the classification between MACEs and no MACEs, and a Cox regression analysis was then used to evaluate the effects of the cardiac magnetic resonance (CMR)-derived parameters on the occurrence of MACEs in the AM patients. RESULTS: Of the 91 AM patients (34.9±18.6 years; 51 males), 13 (14.3%) experienced MACEs during the 1-year follow-up period. In our study, LA longitudinal strain parameters, including reservoir, conduit, and booster function, were significantly reduced in the AM patients in the MACE group compared to the non-MACE group. Specifically, LA reservoir strain was 44.4% (interquartile range, 31.1-66.1%) and 20.6% (interquartile range, 9.9-33.1%) (P=0.002), conduit strain was 22.6% (interquartile range, 15.8-35.1%) and 10.5% (interquartile range, 4.7-13.0%) (P=0.003), and booster strain was 21.4%±14.7% and 10.6%±7.7% (P=0.004) in the non-MACE group and the MACE group, respectively. Among the parameters, reservoir LA longitudinal strain was valuable in diagnosing the development of MACEs in the AM patients [area under the curve (AUC) =0.772, P<0.05], and the survival rate was higher in those with reservoir LA longitudinal strain >25.6%. CONCLUSIONS: CMR-derived LA reservoir strain could be used to predict the long-term survival prognosis of AM patients.