OBJECTIVE Due to uncertainty in the clinical implications of slow coronary flow (SCF), we aimed to investigate the clinical features and mid-term outcome of the Iranian patients with the slow coronary flow phenomenon. METHODS During a four-year period from January 2005 to December 2009, out of 3523 consecutive patients who underwent coronary angiography in the Tehran Heart Center, 325 patients with no stenosis, ectasia, or aneurysm were enrolled in the study. Among them 81 (2.2%) patients were diagnosed with SCF. Baseline characteristics, lab parameters, coronary risk factors and mid-term outcome were described, consequently. RESUITS: Typical chest pain was the most frequent complaint in both groups (normal flow; 118 (48.4%) vs slow flow; 45 (55.6%)). RCA was the most frequently involved vessel for coronary slow flow followed by LCX and LAD and the combination of LCX and LAD involvement for coronary slow flow accounts for 27.2% of cases and three vessel involvement counts for 23.5%. Most patients experienced no symptoms during the follow-up period (NI; 66.4% vs slow flow; 59.3%). However, three patients (3.7%) in the SCF group who underwent a second angiography 2-4 years later, were redefined as slow coronary flow. CONCLUSIONS We could not show any significant difference with respect to initial presentation, coronary risk factors and even mid-term outcome of these patients in comparison to the normal group. However, due to the persistence of the SCF phenomenon even after 2-4 years in the second angiography of our three patients, it seems that slow flow might be a permanent rather than a transient manifestation.