Abstract: Primary percutaneous coronary intervention (PCI) is the preferred treatment for ST segment elevation myocardial infarction. Although there is restoration of coronary flow after PCI, no-reflow phenomenon is frequently observed and may lead to poor prognosis. The pathogenic mechanisms that cause this phenomenon are complex and interrelated. A better understanding of these mechanisms could promote the development of individualized prevention and treatment strategies. Diagnosis of ‘no-reflow’ can be made using angiography, myocardial contrast echocardiography or cardiovascular magnetic resonance. A number of drugs may improve no-reflow experimentally and clinically, but some have not yet been associated with conclusive improvements in clinical outcome.