Abstract Aims The Tpeak-Tend interval on electrocardiogram may be a predictor of worse outcomes in Takotsubo syndrome (TTS), but the mechanisms have not been fully determined. This study aimed to investigate the relationships between the corrected Tpeak-Tend (cTp-e) interval and coronary microvascular-dysfunction (CMD) assessed by the angiography-derived index of microvascular resistance (Angio-IMR) and the in-hospital prognosis in patients with TTS. Methods and results We retrospectively evaluated 111 consecutive patients admitted for TTS who underwent coronary angiography at Kindai University Hospital from October 2009 to July 2023. The Tpeak-Tend interval was defined as the time interval between the peak and the end of the T wave in electrocardiogram lead V5 on admission. Angio-IMR was assessed from aortic pressure, quantitative flow ratio (QFR), vessel length and hyperemic velocity using the formula described in validation studies. QFR, vessel length and hyperemic velocity was derived from coronary angiography and QAngio XA 3D software package. The degree of CMD was assessed by the maximum Angio-IMR value in each of the three coronary arteries. The primary endpoint was the relationship between the grade of a prolonged cTp-e interval on admission and Angio-IMR. The secondary endpoint was the relationship between the grade of a prolonged cTp-e interval on admission and in-hospital adverse cardiovascular events (composite of acute heart failure, cardiogenic shock, life-threatening arrhythmia, thrombotic events, stroke and all-cause death). The median age was 77.5 [71.0–83.0] years, and most patients were women (82.0%). The median cTp-e interval was 114.5 [91.2–147.0] ms. The patients were categorized according to the tertiles of the cTp-e interval (T1: 52.4–96.9 ms; T2: 100.1–129.1 ms; T3: 131.7–309.8 ms). There was a stepwise increment in the values of maximum Angio-IMR in each of the three coronary arteries in tertiles of the cTp-e interval (T1 vs. T2 vs. T3: 16.1 [14.7–19.3] vs. 21.8 [16.0–31.1] vs. 29.0 [27.2–31.9], P < 0.001). In-hospital adverse cardiovascular events occurred in 53 of 111 patients (47.7%). There was a stepwise increment in the incidence of in-hospital adverse cardiovascular events in tertiles of the cTp-e interval (T1 vs. T2 vs. T3: 27.1% vs. 54.1% vs. 62.2%, P = 0.007). The multivariable analysis showed that prolonged cTp-e interval (OR: 1.30; 95% CI: 1.12–1.56; P < 0.001) was independent predictors of in-hospital adverse cardiovascular events. Conclusions The Tpeak-Tend interval on admission reflected CMD and predicts in-hospital adverse cardiovascular events in patients with TTS.