Background: Tei index (TI) is a combined myocardial performance index, which was found to be more sensitive for overall cardiac dysfunction than systolic or diastolic parameters alone. Currently, there is only limited evidence for this measure in the context of myocarditis. Thus, TI could add additional benefits to conventional diagnostic workup. Methods: TI of patients with myocarditis (n = 40), acute coronary syndrome (n = 29) and controls (n = 50) was retrospectively analyzed concerning its discriminatory ability for myocarditis. Results: TI was most pathological in patients with myocarditis (median 0.41 vs. 0.35 vs. 0.31, p < 0.0001). Its discriminatory ability was better than that of EF or E/e’ (AUCs: TI: 0.71, p < 0.0001; EF: 0.57, p = 0.112; E/e’: 0.64, p = 0.983), which was also verified in logistic regression analysis (B(SE) = 0.81(0.23), p = 0.0004). The association of TI with myocarditis remained significant even after correction for confounders in propensity score weighted analysis. Conclusions: The TI showed a better discriminatory ability for myocarditis than conventional echocardiographic parameters. Since TI is easily conducted, it might be a helpful adjunctive tool to supplement conventional diagnostic modalities in patients with suspected myocarditis.