Background: The impact of a mechanical reperfusion strategy beyond a 24-hour cut-off is still unsettled. Optimal management for these patients remains uncertain. Purpose: We sought to investigate the effect of delayed primary percutaneus coronary intervention (p-PCI) – 24 to 48 hours after symptom onset-for patients with ST-segment elevation myocardial infarction (STEMI) not undergoing timely reperfusion therapy. Methods: We conducted a cohort study of 1822 STEMI first-day survivors who were admitted with a diagnosis of STEMI, but did not receive any mechanical or pharmacological reperfusion therapy within 24 hours from symptom onset. We used multivariable logistic regression combined to landmark analysis to evaluate the effect of delayed p-PCI on in-hospital mortality and incidence of severe left ventricular dysfunction (LVD; ejection fraction