BACKGROUND The coronary slow flow phenomenon is an angiographic finding characterized by delayed distal vessel opacification in the absence of significant epicardial coronary disease, and is an important clinical entity because it may be the cause of angina at rest or during exercise, acute myocardial infarction, and hypertension. The pathophysiological mechanisms of the coronary slow flow phenomenon remain undetermined. Endothelial dysfunction and microvascular dysfunction have been suggested as underlying mechanisms. The slow coronary flow (SCF) phenomenon is considered to be a form of early phase atherosclerosis in some studies.A study of patients with SCF was conducted to determine the associated clinical and angiographic properties. METHODS Eighty-five patients with SCF and 85 control subjects without SCF were included in the study. All subjects had angiographically proven normal coronary arteries. Coronary flow patterns of the latter were determined by the thrombolysis in myocardial infarction frame count method. Clinical and angiographic characteristics of the patients were obtained from case records. RESULTS Patients with SCF had higher total cholesterol, and LDL-C levels. Body mass index (BMI) was higher and metabolic syndrome was more frequent in SCF compared to control subjects. Patients with SCF were more symptomatic than the control group, and hospital admissions were also more frequent. BMI correlated statistically significantly, but weakly, with mean TIMI frame count for the 3 coronary arteries. CONCLUSIONS In this study we demonstrated that patients with SCF had a significant metabolic disarrangement compared to the control group. Patients with SCF have a high incidence of metabolic syndrome which leads to development of coronary microvascular dysfunction via several mechanisms.