The aims were to describe the clinical and subclinical characteristics of beta thalassemia patients with reduce EF% on Doppler echocardiography in Thai Nguyen Central Hospital. Methods: A cross-sectional study was performed on 67 patients with thalassemia treated at the Clinical Hematology Department, Thai Nguyen Central Hospital from 1/2021 to 1/2022. Results: The female rate was higher than male rate; the majority of patients are ethnic minorities (71.6%); the age group <15 accounted for the highest percentage (50.7%), the mean age of diagnosis of the disease group was 2(±2) lower than the control group. Common clinical symptoms were: dizziness (41%) and fatigue (40%). The test showed that: mean Hb, mean Bil TT & TP, mean SGOT of the the disease group with reduced left ventricular ejection fraction lower than the control group; the ultrasound index of the disease group was also lower than the control group. There was a statistically significant difference in the mean age of diagnosis, the frequency of blood transfusions ≥5 times/year in the group of thalassemia patients with reduced left ventricular ejection fraction with the control group (p<0.05); Mean EF (53.16±1.12), mean FS (31.16±2.46) evaluating left ventricular systolic function of the disease group were lower than the control group, with p<0.05; There was a statistically significant difference between the disease group with blood ferritin ≥ 2500 ng/ml of the patient group and the control group, with p< 0.05.