Although type 2 diabetes mellitus (T2DM) individuals easily develop three-vessel disease (3VD) coronary artery disease (CAD), there is very little information available about their left ventricle (LV) functions. The purpose of this study is to evaluate the LV function using two-dimensional speckle tracking echocardiography (2-D STE) in T2DM patients with 3VD.One hundred and three consecutive patients with confirmed 3VD CAD were enrolled and divided into two groups, while 53 patients with DM and 50 patients without. The control group was composed of 30 age- and sex-matched healthy individuals. All patients underwent 2-D STE and standard echocardiograms. The durations of DM and the level of HbA1c were also recorded.Between the 3VD-DM and 3VD-non-DM groups, normal echocardiography did not reveal any appreciable differences. However, patients with 3VD-DM had significantly lower global longitudinal strain (GLS) than those with 3VD-non-DM (15.87 ± 2.51 vs.17.56 ± 2.72, p < .05) by 2-D STE strain measurement. Besides, patients whose duration of DM excess 5 years showed significant lower GLS than those with less than 5 years duration (14.25 ± 2.31 vs. 16.65 ± 1.96, p = .007). However, there was no difference in GLS between the 3VD-DM patients with HbA1c ≥ 7% and HbA1c < 7%.Compared to patients with 3VD alone, those with 3VD-DM have a lower cardiac function. In 3VD-DM patients, the duration of DM is a significant factor that contributes to cardiac function deterioration, whereas, the glucose control state has limited influence.© 2023 The Authors. Echocardiography published by Wiley Periodicals LLC.