Despite optimal epicardial recanalization, primary angioplasty for STEMI is still associated with suboptimal reperfusion in a relatively large proportion of patients. The aim the current study was to evaluate the impact of preprocedural TIMI flow on myocardial scintigraphic infarct size among STEMI undergoing primary angioplasty. Our population is represented by 793 STEMI patients undergoing primary PCI. Infarct size was evaluated at 30 days by technetium-99m-sestamibi. Poor preprocedural TIMI flow (TIMI 0-1) was observed in 645 patients (81.3%). Poor preprocedural TIMI flow was associated with more hypercholesterolemia (p = 0.012), and a trend in lower prevalence of diabetes (p = 0.081). Preprocedural TIMI flow significantly affected scintigraphic and enzymatic infarct size. Similar findings were observed in the analysis restricted to patients with postprocedural TIMI 3 flow. The impact of preprocedural TIMI flow on scintigraphic infarct size was confirmed when the analysis was performed according to the percentage of patients above the median (p < 0.001) and after adjustment for baseline confounding factors (Hypercholesterolemia and diabetes) [adjusted OR (95% CI) for pre preprocedural TIMI 3 flow = 0.59 (0.46-0.75), p < 0.001]. This study shows that among patients with STEMI undergoing primary angioplasty, poor preprocedural TIMI flow is independently associated with larger infarct size.