This study sought to determine the prevalence as well as clinical and electrocardiographic correlates of patients referred for primary percutaneous coronary intervention (PCI) who had angiographically normal coronary arteries. Data for 690 consecutive patients with ST-elevation myocardial infarction (STEMI) referred for primary PCI within a metropolitan area health service were reviewed. Characteristics of patients with angiographically normal coronary arteries (n = 87; 13%) were compared with patients with angiographically shown culprit lesions (control group; n = 594). Nine patients with significant coronary disease, but no identifiable culprit lesion, were excluded. Electrocardiograms (ECGs) from both groups were reviewed by 2 cardiologists blinded to angiographic findings. Patients in the normal coronaries group were younger and had fewer risk factors. On expert review of ECGs, 55% of patients in the normal coronaries group had ST-elevation criteria for STEMI (vs 93% in the control group; p <0.001), but the ECG was considered consistent with a diagnosis of STEMI by both observers in only 33% (vs 92% in the control group; p <0.001). Left branch bundle block independently correlated with normal coronary arteries on multivariate analysis (odds ratio for STEMI 0.016, 95% confidence interval 0.004 to 0.064, p <0.001). The discharge diagnosis in the normal coronaries group was predominantly pericarditis (n = 72; 83%). In conclusion, the prevalence of angiographically normal coronary arteries in patients referred for primary PCI was 13%. Electrocardiographic correlation suggested that this can be reduced by adherence to conventional electrocardiographic criteria for STEMI diagnosis and review of ECGs by experienced clinicians.