Background: Coronary artery bypass grafting (CABG) is a surgical procedure used in the treatment of coronary artery disease and to improve heart function. Right ventricular (RV) function is unclear based on myocardial velocities before and after coronary artery bypass graft surgery. RV dysfunction is a known cause of hypotension in early CABG surgery. The diastolic function has been shown to be a significant contributor to mortality and cardiac morbidity in recent years. Our study aimed to assess RV diastolic dysfunction after CABG surgery. Methods: Forty-four patients with the two-vessel disease (2 VD), small vessel disease (SVD) and three-vessel disease (3 VD) facial ischemia candidates for CABG surgery were studied. All patients underwent colour Doppler and RV strain echocardiography before and one month after CABG surgery, and patients’ RV function indices were calculated. Data analysis was performed using SPSS 21 software and a value of P<0.05 was considered statistically significant. Results: Out of forty patients, the male to female ratio was 32:8 and their mean age was 65.17 ± 7.87 years and their mean body mass index was 25.59± 3.20. Four patients were operated on without pumps. One month after CABG, systolic pulmonary artery pressure (SPAP), left ventricular ejection fraction (LVEF) and RV Diameter indexes increased significantly. Fractional area change (FAC), RV global longitudinal strain (GLS), Tissue Doppler imaging systolic wave (SM), RV myocardial perfusion imaging (MPI) and Tricuspid annular plane systolic excursion (TAPSE) decreased, which was less in the 3VD group than in the 1VD/2VD group (P <0.001). There was no significant difference between RV diastolic diameter (RVDD) and left ventricular diastolic diameter (LVDD) before and one month after CABG (P <0.05). Additionally, no significant correlation was detected between changes in RV strain and pump connection time. Conclusion: RV diastolic function is significantly reduced after CABG surgery. Surgery without the pump can certainly not eliminate this dysfunction and be effective in reducing its severity.