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Background Takotsubo cardiomyopathy (TTC) is an acute, life-threatening condition which is typically induced by stress and manifested by chest pain and ECG changes. The TTC prevalence among patients (pts) with acute coronary syndrome is 1.7–2.2%. The mortality rate from TTC is up to 8%. TTC is clinically indistinguishable from acute myocardial infarction (AIM). Differential diagnosis of TTC and AIM remains an unresolved problem. Recent studies have shown the differences in profiles of plasma microRNAs inTTC and AIM. Purpose To evaluate the possibility of differentiating TTC and AIM using a PCR-based semi-quantitative analysis of mRNAs, the plasma levels of which had been shown to be increased in patients with AIM (miR-1, miR-208a, miR-133a, miR-499a) and TTC (miR-16, miR-26a). Methods Plasma from 38 pts was used: 13 pts with confirmed TTC (12 women, 1 man), 25 pts with AIM (9w, 16m). For 10 pts with AIM, blood was collected twice: at 6 and 24 hours after the heart attack. The control arm comprised 40 healthy people from the same age group (12w, 28m). Plasma was obtained using the Cell-Free DNA blood collection tubes. Nucleic acids were separated using a modified Boom method. A semi-quantitative assessment of the mRNA levels was performed using dCq method with stem-loop qRT-PCR. Normalization for spiked synthetic cel-miR-39 and endogenous miR-23a was performed. Control of hemolysis was performed by measuring the ratio of miR-451 (specific for RBCs) and miR-23a (absent from RBCs). The statistical significance of differences between mRNA levels was assessed using Mann–Whitney test. Results No significant differences in the levels of miR-16, miR-26a and miR-208a in TTC group and control group have been found. Pts with AIM significantly differed from pts with TTC (p=0.0038 and 0.0002, respectively) and control pts (p=3.1x10–9 and 2,66x10–10) with the increased levels of cardiac-specific miR-1 and miR-133a. As compared to plasma levels at 6 hours after the heart attack, at 24-hour point the levels of these mRNAs were markedly reduced in 9 of 10 pts (mean reduction was 22.3-fold for miR-133a and 7.5-fold for miR-1). The correlation between changes in the levels of these mRNAs was high (Spearman correlation coefficient=0.89). Significant differences in plasma levels of miR-133a between pts with AIM and TTC were maintained even if blood was collected after 24 hours (p=0.007). For miR-16 and miR-26a, no significant differences between pts with AIM and TTC were found. The results of analysis of these mRNAs are affected to a substantial degree by the residual hemolysis due to their high content in blood cells. Conclusions It was shown that measuring the plasma levels of mRNAs miR-1 and miR-133a allows to distinguish TTC from AIM by excluding the diagnosis of TTC. The differential diagnosis is possible only within several hours after acute clinical symptoms and requires proper normalization and full compliance with the technical specifications.