Background and Objective Subjects with diabetes and periodontitis are at high risk of cardiovascular events, while the subclinical alterations of cardiac function in this cohort remain unclear. This cross‐sectional study investigated the association of periodontitis with left ventricle (LV) structural and functional abnormalities in subjects with type 2 diabetes mellitus (T2DM). Material and Methods A total of 115 subjects with T2DM were divided into Control group (n = 32) with no or mild periodontitis, and the rest with moderate to severe chronic periodontitis (CP) were further categorized into CP‐1 (n = 41) and CP‐2 (n = 42) based on disease severity. Echocardiography was performed to precisely assess (a) LV hypertrophy by LV mass index (LVMi); (b) LV diastolic function by tissue Doppler imaging index E/e’ ratio; and (c) LV systolic function by speckle tracking derived global longitudinal strain (GLS). Results Overall, a linear trend in LVMi, E/e’, and GLS existed among the Control, CP‐1, and CP‐2 groups, respectively (P < 0.05). After adjustments of multiple confounders, CP‐2 subjects showed significantly higher E/e’ (log scale, 2.22 ± 0.05 vs 2.07 ± 0.06, P < 0.01) and GLS (−17.42 ± 0.46% vs −18.95 ± 0.54%, P < 0.05) than the Controls. Multivariate analysis revealed that sites% with probing depth ≥4 mm and sites% with clinical attachment loss ≥5 mm were independent indicators for E/e’ (β = 0.005 and β = 0.002, P < 0.01) and GLS (β = 0.03 and β = 0.02, P < 0.05) , respectively. Moreover, the number of missing teeth was significantly associated with LVMi (β = 0.01, P < 0.01). Conclusion This study provides the first evidence that severe periodontitis is significantly associated with the exacerbation of LV diastolic and systolic dysfunction in subjects with T2DM.