During primary PCI, stent deployment and post-dilatation are associated with no-reflow. The mechanisms for no reflow include distal embolization of thrombus, enhanced thrombus formation and vascular spasm. No reflow is associated with risk factors such as prolonged duration of ischaemia, heavy thrombus burden, persistent ST elevation and long stent length. ACTIVE HYPOTHESIS: once normal antegrade flow has been re-established with initial aspiration thrombectomy and/or balloon angioplasty at the beginning of primary PCI, compared with usual care with direct stenting, a strategy of deferred stenting for 4 -16 hours to permit the beneficial effects of normalized coronary blood flow and anti-thrombotic therapies will reduce the incidence of no reflow in at-risk STEMI patients. DESIGN: In consecutive STEMI patients with risk factors for no reflow and who have given informed consent, when normal flow has been established (TIMI 3) by initial aspiration thrombectomy and/or balloon angioplasty, participants will be randomized to deferred stenting or usual care with direct stenting. All patients will receive dual anti-platelet therapy. Patients who are randomized to deferred stenting will receive intravenous glycoprotein IIbIIIa inhibitor and anti-coagulation with low molecular weight heparin. Patients who are screened and not eligible to be randomized will be prospectively entered into a registry. Study assessments for feasibility, safety and efficacy will be prospectively performed. An independent clinical event committee will review all serious adverse events. Study endpoints will be subject to core laboratory analyses. The study is intended to inform the design of a larger multicentre clinical trial.