Introduction: More than 50% of patients with acute myocardial infarction (AMI) have multivessel coronary artery disease. Evidence regarding the optimal treatment of the non-culprit lesions (NCL) is still limited. Revascularization of the moderate NCL associated with improved outcome, if significant ischemia was detected by a non-invasive test such as dobutamine stress echocardiography (DSE) before the intervention. Contrarily the prognostic value of fractional flow reserve (FFR) is equivocal in this clinical setting.In our prospective trial, we compared FFR measurements to the standard method of DSE in the evaluation of NCL.Methods: Patients with one or more moderate (40-80 % diameter) NCL were included in our study after primary coronary intervention. These NCLs were examined by DSE and FFR after the index episode within 3 months. DSE and FFR was performed within 4 weeks. If both the DSE and the FFR was negative or there was discordance between the tests, the patients were kept on optimal medical treatment.Results: Sixty-nine consecutive AMI patients (56 males, age: 59±10 yrs, EF: 48.4±7.1%) with 82 NCLs (48 LAD, 7 LCX, 14 RCA; SYNTAX: 17.1 ± 5.9) were enrolled from December 2014 to December 2016. Most of them (92%) were in CCS I class.The diagnostic accuracy of FFR was 64.6 % compared to DSE. The positive and negative predictive value of FFR was 14.8 and 89.1 % respectively. The sensitivity and specificity of FFR was 40 and 68 %. In comparison, there was no significant correlation between the DSE and FFR results.Conclusions: The good negative predictive value of FFR makes it a useful single functional test to decline revascularization of the NCL. In positive cases an additional functional test might be needed to identify NCL for revascularization.The clinical significance of the discordance between FFR and DSE should be determined by follow up studies.