The study aimed to evaluate the morphological changes in erythrocytes following the administration of various solutions. Patients who underwent mitral valve (MV) replacement were divided into three groups: the first group received Hydroxyethylcellulose (HEC), the second received gelatin solution (4% succinylated gelatin solution), and the third received 0.9% sodium chloride solution. Blood samples were collected at 90 minutes, 24, and 48 hours post-resuscitation (ICU), and before discharge. Healthy patients' blood served as the control. The express technique of the "thick drop" (EMTD) was used to assess erythrocyte shape shifts, measuring the ratio of normal and pathological forms within 10-15 minutes using a DN-300M microscope. Before using the solutions, the pathological forms of erythrocytes were significantly higher in all groups compared to the control group. The control group had over 89.8% discocytes, while the number significantly decreased in MV patients pre-operation. Post-treatment with HEC and Gelatin solution, the number of discocytes increased slightly, whereas the third group (sodium chloride) showed no significant change. The number of echinocytes and stomatocytes varied across the groups, with the third group showing minimal improvement. The findings indicated that HEC and gelatin solution improved the ratio of discocytes to pathological forms better than sodium chloride. The most promising plasma-stimulating agents for surgical patients, particularly those with heart disease, are colloids and balanced crystalloid solutions. Their composition closely mimics blood plasma, providing optimal hemodynamic stability and tissue perfusion, thus supporting better postoperative recovery and critical care management.