The aim of this study is to assess the prognostic value of mechanical dyssynchrony defined as the standard deviation of the time to peak longitudinal strain (SD T2P LS) in predicting the development of heart failure (HF) after an ST-segment elevation myocardial infarction (STEMI). Three hundred and seventy-three patients were admitted with STEMI and treated with primary percutaneous coronary intervention. Left ventricular (LV) mechanical dyssynchrony was examined through speckle tracking echocardiography and defined as SD T2P LS. The association with the outcome of HF hospitalization was assessed using Cox proportional hazard models. During a median follow-up of 5.12 years, 144 patients (38.6%) were admitted due to HF. Worse dyssynchrony was associated with the outcome in unadjusted and multivariable analysis (multivariable hazard ratio 1.05, 95% confidence interval 1.00-1.10, p-value 0.039, per 10 ms increase), but not after further adjustment for LV ejection fraction (LVEF), E/e' and global longitudinal strain (GLS) (hazard ratio 1.01, 95% confidence interval 1.00-1.07, p-value 0.71, per 10 ms increase), nor in a model only adjusting for GLS (hazard ratio 1.01, 95% confidence interval 1.00-1.06, p-value 0.61, per 10 ms increase). These findings were reproduced in a competing risk analysis treating all-cause mortality as a competing risk. LV mechanical dyssynchrony, as assessed by SD T2P LS is not an independent predictor of post-STEMI HF development and mechanical dyssynchrony does not provide independent prognostic information regarding HF when GLS is known.