BACKGROUND: Global longitudinal strain (GLS) is a robust, well validated and reproducible technique for the measurement of LV longitudinal deformation. We sought to assemble evidence that GLS is an accurate marker in predicting cardiovascular outcomes, compared to LVEF. METHODS: We undertook a systematic review of the evidence from observational studies which compared GLS against LVEF in predicting major adverse cardiac events. The primary outcome was all-cause mortality. The secondary outcome was a composite of cardiac death, malignant arrhythmia, hospitalisation due to heart failure, urgent valve surgery or heart transplantation, and acute coronary ischaemic event. A random effects model was used to combine HR and 95% CIs. A meta-regression was undertaken to assess the impact of potential covariates. RESULTS: Data were collated from 16 published articles (n=5721 adults) comprising 15 prospective and 1 retrospective observational studies. The underlying cardiac conditions were heart failure, acute myocardial infarction, valvular heart disease, and miscellaneous cardiac diseases. Mortality was independently associated with each SD change in the absolute value of baseline GLS (HR 0.50, 95% CI 0.36 to 0.69; p<0.002) and less strongly with LVEF (HR 0.81, 95% CI 0.72 to 0.92; p=0.572). The HR per SD change in GLS was associated with a reduction in mortality 1.62 (95% CI 1.13 to 2.33; p=0.009) times greater than the HR per SD change in LVEF. CONCLUSIONS: There is strong evidence of the prognostic value of GLS, which appears to have superior prognostic value to EF for predicting major adverse cardiac events.