The primary goal in patients with ST-elevation myocardial infarction (STEMI) is the restoration of myocardial tissue-level perfusion. In a variable proportion of patients with STEMI, however, microcirculatory impairment may persist after epicardial coronary artery recanalization. This phenomenon is known as "myocardial no-reflow". Of note, no-reflow is associated with a worse prognosis both at short- and long-term follow-up. Depending on the population under study and the diagnostic technique used for its detection, the incidence of no-reflow ranges from 5 to 50%. No-reflow can be directly assessed in the cath-lab in several ways, including angiographic Thrombolysis in Myocardial Infarction (TIMI) flow grade assessment and more complex angiographic indexes, such as TIMI frame count, TIMI perfusion grade, myocardial blush grade, or by direct invasive assessment of coronary flow. After the cath-lab, both the evaluation of electrocardiographic ST-segment resolution and imaging techniques, as myocardial contrast echocardiography or cardiac magnetic resonance, are able to monitor no-reflow evolution, with imaging playing a crucial role in its quantification. In this article, we review indexes of no-reflow used both in the cath-lab and thereafter.