Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, resulting in uncoordinated contractions and a decrease in the efficiency of blood pumping by about 10- 20%. This condition can lead to increased stiffness of the left atrium (LA) walls, facilitating the formation of areas of blood stasis and potential thrombus generation, especially in the left atrial appendage (LAA), increasing the risk of ischemic events. AF is often a consequence of high blood volume in the atria due to heart valve lesions or ventricular insufficiency, which can lead to blood accumulation in the atria. Ventricular dysfunctions, such as diastolic dysfunction (DD), are correlated with the occurrence of AF, affecting cardiac pumping efficiency and resulting in significant hemodynamic changes. In the present paper, a numerical study time using Computational Fluid Dynamics (CFD) was performed for the first to analyze the effects of concomitant occurrence of DD and AF on hemodynamic indicators (Time-Averaged Wall Shear Stress, TAWSS, Oscillatory Shear Index, OSI, and Relative Residence Time, RRT) of thrombus-prone zones. Five cases were investigated: a healthy case and four AF cases with different stages of DD: normal, altered relaxation, pseudonormal and restrictive flow patterns, reproduced by changing the blood flow profile in the pulmonary veins. The results revealed that as DD progressed, the average blood velocity in the LA decreased, increasing blood stasis (increased RRT). The presence of AF and DD also amplified blood recirculation (increased OSI), especially in cases of pseudonormal and restrictive flow, due to the complex morphology of the LAA. Additionally, an increase in TAWSS on the atrial wall during LAA contraction was observed, indicating increased blood movement. However, in cases of AF with DD, there was a significant decrease in TAWSS and increments in OSI and RRT, especially in the LAA, increasing the risk of thrombus formation.