BACKGROUND: Many patients with stable coronary artery disease (CAD) have no visual segmental wall motion abnormalities and a left ventricular (LV) ejection fraction (LVEF) ≥ 50% at rest despite significant coronary artery stenosis. Here, the aim was to determine the impact of percutaneous coronary intervention (PCI) on LV function assessed by enhanced echocardiography in patients with stable CAD with or without diabetes mellitus type 2 and a preserved LVEF. METHODS: Sixty-six consecutive patients with CAD and LVEF ≥ 50%, admitted to the hospital for planned coronary angiography, were prospectively assessed. PCI was performed for coronary artery stenosis > 70%. CAD extent was assessed using SYNTAX and EXTENT scores. To assess LV function, LVEF, global longitudinal strain (GLS), and LV peak systolic myocardial velocity (S') were measured and Tei index was calculated before and 3 months after PCI. RESULTS: Before PCI, LVEF, GLS, and Tei index were significantly worse in diabetic patients. LV functional indices improved significantly after PCI in all patients (p < 0.001). Multivariate linear regression analyses were performed to evaluate the impact of selected factors on LV function after PCI expressed as changes (D) of LVEF, GLS, S', and Tei index. LV function improvement expressed as DGLS was associated only with SYNTAX score. Higher SYNTAX scores were related to greater GLS improvement (b = 0.003, 95% confidence interval: 0.0004-0.005; p = 0.02). CONCLUSIONS: Percutaneous coronary intervention significantly improved LV function in diabetic and non-diabetic CAD patients with preserved LVEF. Enhanced echocardiography allowed an assessment of subtle changes in LV function.