Residual platelet reactivity (RPR) after clopidogrel loading, measured by the VerifyNow assay, has been shown to predict 12-month clinical events in patients with acute coronary syndromes. However, links between coronary angiographic findings and outcome in patients with ST-elevation myocardial infarction (STEMI), with RPR have not been reported. We investigated whether RPR is associated with the amount of intracoronary thrombus burden (TB) in patients with STEMI undergoing unexpectedly-delayed primary percutaneous coronary intervention (pPCI). Moreover, we evaluated whether RPR might influence coronary flow and myocardial perfusion immediately post-pPCI.