Background Myocardial tissue-level perfusion failure is associated with adverse outcomes following ST-elevation myocardial infarction (STEMI) despite successful epicardial recanalization. We have developed a new quantitative index-thrombolysis in myocardial infarction (TIMI) myocardial perfusion frame count (TMPFC)-for assessing myocardial tissue level perfusion. However, factors affecting this novel index of myocardial perfusion are currently unknown.Methods A total of 255 consecutive STEMI patients undergoing primary angioplasty were enrolled. Myocardial tissue level perfusion was assessed by TMPFC, which measures the filling and clearance of contrast in the myocardium using cine-angiographic frame counting. We differentiate three groups with two cut off values for TMPFC: a TMPFC of 90frames was the upper boundary of the 95% confidence interval (CI) for the TMPFC observed in normal arteries, and a TMPFC of 130 was the 75th percentile of TMPFC.Results STEMI patients with TMPFC ＞130 frames (68 patients, 26.7%) had higher clinical and angiographic risk factor profiles as well as a higher 30-day MACE rate compared with those with TMPFC ≤90 frames and those with TMPFC ＞90and ≤130 frames. Multivariable analysis identified that the independent predictors of TMPFC ＞130 frames were age ≥75years (OR 2.08, 95% CI 1.21 to 3.58, P=0.007), diabetes (OR 1.37, 95% CI 1.01 to 1.86, P=0.042), Killip class ≥2 (OR1.52, 95% CI 1.05 to 2.21, P=0.027), and prolonged pain-to-balloon time (OR 1.73, 95% CI 1.07 to 2.79, P=0.013).TMPFC ＞130 frames was identified as the strongest independent predictor of 30-day major adverse cardiac event (MACE) (OR 2.77, 95% CI 1.21 to 6.31, P=0.008), along with age ≥75 years (OR 2.19, 95% CI 1.11 to 4.33, P=0.016),female gender (OR 1.67, 95% CI 1.03 to 2.70, P=0.038), and Killip class ≥2 (OR 1.83, 95% CI 1.07 to 3.14, P=0.021).Conclusions STEMI patients with poor myocardial perfusion assessed by TMPFC had higher risk factor profiles.Advanced age, diabetes, higher Killip class, and longer ischemia time were independent predictors of impaired TMPFC after primary percutaneous coronary intervention. These results emphasize that particular attention should be paid on myocardial microvascular reperfusion in STEMI patients with these risk factors.