Effective reperfusion of ischemic myocardium is the final aim of both pharmacological and mechanical reperfusive strategies in patients with ST-segment elevation myocardial infarction. More effective reperfusion is related to better prognosis. In contrast, ineffective reperfusion (no reflow) has been showed to be related to an increased rate of adverse events in the flow-up. Several techniques can be used to assess the effectiveness of reperfusion, and the evolved over the last decades according to the treatment methods but also to technological advancements. ST-segment resolution represented the only way to assess reperfusion in the era of pharmacological treatment. Later, angiographic assessment became the gold standard to assess reperfusion after primary percutaneous coronary intervention. In the last years, cardiac magnetic resonance showed improved accuracy and prognostic stratification ability compared with angiography. However, in clinical practice, coronary angiographic still remains the more widely used assessment technique for no reflow.