['We assessed the relationship between fibrin clot properties and the no-reflow phenomenon after primary coronary intervention (PCI).', 'Epicardial blood flow was assessed by TIMI scale and corrected TIMI frame count (cTFC), and perfusion by TIMI Myocardial Perfusion Grade (TMPG) after PCI during ST-segment elevation myocardial infarction (STEMI). Fibrin clot permeability (K(s)) and susceptibility to lysis in assays using exogenous thrombin (t(50%)) and without thrombin (t(TF)) were determined in 30 no-reflow patients (TIMI < or = 2) and in 31 controls (TIMI-3) after uneventful 6 to 14 months from PCI. Patients with TIMI < or = 2 had lower K(s) by 18% (P<0.0001) and prolonged fibrinolysis by 33% for t(50%) (P<0.0001) and by 45% for t(TF) (P<0.0001). cTFC was correlated with K(s) (r=-0.56, P<0.0001), t(50%) (r=0.49, P<0.001), and t(TF) (r=0.54, P<0.001). K(s) increased in a stepwise fashion with TIMI flow (P<0.0001) and TMPG (P<0.0001), whereas both fibrinolysis times decreased with TIMI flow (P<0.0001 for both) and TMPG (P<0.01 for both). Multiple regression models showed that only K(s) and fibrinogen were independent predictors of cTFC (P<0.05 for both), TIMI < or = 2 flow (P<0.05 for both) and TMPG-0/1 (P<0.05 for both).'] Is no-reflow phenomenon after acute myocardial infarction associated with reduced clot permeability and susceptibility to lysis?