This study investigated the impact of arterio-venous shunts on blood parameters in a rat model of heart failure. Researchers divided 28 rats into three groups, including a control group, an aorto-caval group (AC) with a side-to-side aorto-caval anastomosis, and a femoral arterio-venous (FAV) group with a femoral vein-to-artery connection. Blood tests showed an early increase in white blood cell and platelet counts across groups, with red blood cell counts initially dropping then rising. Notably, red blood cell deformability worsened, particularly in the AC and FAV groups, alongside increased red blood cell aggregation, especially in the FAV group. These results suggest that arterio-venous shunts can worsen blood flow and contribute to heart failure pathophysiology through hematological and micro-rheological changes.