After reopening of the infarct related artery by primary percutaneous coronary interventions (PPCI), microvascular damage at the related myocardial territory is not terminated immediately. This ongoing nature of microvascular damage leading to myocardial malperfusion is related to final infarct size. However, time course of the microvascular impairment /obstruction after PPCI in patients presented with ST-elevating acute myocardial infarction (STEMI) is not known. Routine primary percutaneous coronary interventions (PPCI) for ST-elevation acute myocardial infarction (STEMI) includes balloon angioplasty (or thrombectomy) followed immediately by stent implantation. However, stent implantation performed in this thrombotic setting may lead to a further microvascular damage by causing more distal embolisation and by inducing distal microvascular spasm by stretching the coronary vessel wall. Furthermore, sudden exposure of distal microcirculation to a high distal intracoronary pressure achieved by immediate stent implantation may exaggerate myocardial oedema which contributes microvascular damage substantially by external compression. However, results of studies investigating the efficacy of delayed stenting (24-48 hours later) in patients in whom TIMI -3 flow was achieved after balloon angioplasty were inconsistent.