BackgroundMyocardial injury post-stroke is a common sequela of acute stroke. Triglyceride-glucose index (TyG index), a valuable surrogate indicator of insulin resistance, has been suggested to be closely related to cardiovascular outcomes. However, it is unknown whether the TyG index is independently associated with a higher risk of myocardial injury post-stroke. We therefore investigated the longitudinal association between TyG index and risk of myocardial injury post-stroke in older patients with first-ever ischemic stroke and no prior cardiovascular comorbidities.MethodsWe included older patients with first-ever ischemic stroke and no prior cardiovascular comorbidities between January 2021 to December 2021. The individuals were stratified into low and high TyG index groups according to the optimal cutoff value with TyG index. We performed logistic regression analysis, propensity score matching (PSM) analysis, restricted cubic spline analysis, and subgroup analyses to explore the longitudinal association between TyG index and risk of myocardial injury post-stroke.ResultsWe included 386 individuals with a median age of 69.8 years (interquartile range: 66.6, 75.3). The optimal TyG index cut-off for predicting myocardial injury post-stroke was 8.9 (sensitivity 67.8%; specificity 75.5%; area under curve 0.701). Multivariate logistic regression analysis revealed that the risk of genesis of myocardial injury post-stroke increased with elevated TyG index (odds ratio [OR], 2.333; 95% confidence interval [CI], 1.201–4.585;P= 0.013). Furthermore, all covariates were well balanced between the two groups. The longitudinal association between TyG index and myocardial injury post-stroke remained significantly robust (OR: 2.196; 95% CI: 1.416–3.478;P< 0.001) after PSM adjustment.ConclusionIndividuals with an elevated TyG index were more susceptible to having an increased risk of myocardial injury post-stroke. TyG index thus might be served as a complementary approach for optimized-for-risk stratification in older patients with first-ever ischemic stroke and no prior cardiovascular comorbidities.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12877-023-04041-7.