Data presented in this article relates to the research article entitled “Association between QRS duration on prehospital ECG and mortality in patients with suspected STEMI” (Hansen et al., in press) [1]. Data on the prognostic effect of automatically recoded QRS duration on prehospital ECG and presence of classic left and right bundle branch block in 1777 consecutive patients with confirmed ST segment elevation AMI is presented. Multivariable analysis, suggested that QRS duration >111 ms, left bundle branch block and right bundle branch block were independent predictors of 30 days all-cause mortality. For interpretation and discussion of these data, refer to the research article referenced above.