The incidence and timing of sustained ventricular tachycardia or fibrillation (VT/VF) and its impact on outcomes in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI) are poorly understood. To evaluate the association of sustained VT/VF and its timing on the outcomes of patients presenting for primary PCI-an aim not prespecified in the APEX AMI trial.