Background Tei index has been proposed as a noninvasive and simple index that enables the evaluation of global left ventricular (LV) function and prediction of patient prognosis. However, its use to predict complications with acute myocardial infarction (AMI) is not fully investigated. Therefore, the purpose of this study was to investigate whether or not LV Tei index allows noninvasive prediction of complications with AMI. Methods In all, 80 consecutive patients with anteroseptal AMI were enrolled. LV Tei index was measured at the time of admission as ( a − b)/ b, where a is the interval between cessation and onset of mitral filling flow and interval b is the aortic flow ejection time. Subsequent complications including cardiac death, shock, congestive heart failure, ventricular tachycardia/fibrillation, paroxysmal atrial fibrillation/flutter, advanced atrioventricular block requiring pacing, pericardial effusion, and LV aneurysm during the 30 days after the onset of AMI were prospectively evaluated and compared with the initial Tei index at admission. Results Complications developed in 31 of 80 (39%) patients with AMI. The Tei index was significantly increased for patients with complications compared with those without them (0.69 ± 0.16 vs 0.50 ± 0.11, P < .0001). When Tei index ≥ 0.59 was used for the criteria, the sensitivity, specificity, and overall accuracy to predict subsequent complications were 77%, 86%, and 85%, respectively. Conclusion In patients with anteroseptal AMI, LV Tei index at arrival to the hospital in the acute phase allows noninvasive prediction of subsequent complications.