Objectives: Over the last years, the prevalence of heart failure has been slowly increasing due to improved treatment of chronic heart failure and its underlying causes and an aging population. The main reason for an acute heart failure hospitalization is signs or symptoms of congestion for which the first-choice treatment is administration of loop diuretics. This investigation set out to evaluate the effects of different dose of furosemide on biochemical (creatinine, urea, CRP, CK, LDH, ADL and TROP.), and histological (Kidney and Heart) in rabbits. Materials and Methods: The present study has been conducted in the animal house of the pharmaceutical laboratory in Samarra during the period extended from Nov.-Dec., 2022. A total of 20 male rabbits were divided randomly into four groups (4/group): Group (G1) control negative: five rabbits will be administrating with normal saline and animals is euthanized after 4 weeks.; Group (G2) is the normal dose: five rabbits will be administrating with 0.1ml per kg every day for 4 weeks.; Group (G3) of middle dose: five rabbits will be administrating of 0.2 ml per kg every day for 4 weeks.; Group (G4) experimental group over dose: five rabbits will be administrating of 0.4 ml per kg for 4 weeks. Males were anesthetized (by chloroform 5 ml), dissected, and blood samples were taken from the heart in non-heparinized tubes at the conclusion of each treatment and control. (Creatinine, urea, CRP, CK, LDH, ADL and TROP.), were measured by analyzing blood serum samples. Each rabbits have a heart and kidney removed for histological analysis. Results: The results of this study showed that there is no significant difference (p>0.05) in creatinine level between the experimental groups and the control group. While there was Urea, CK, TROP, ALD and a significantly decrease (p<0.05) at the level of LDH, between experimental groups with the control group. Also, the results of this study showed that there is a significant difference (p>0.05) in CRP level between the experimental groups and the control group. In kidney tissue histological studies show in furosemide groups the hypertrophy of the glomeruli and their lobulation and the presence of infiltration of white blood cells on their surface with hemorrhage around the glomeruli, vacuolar degeneration. In heart tissue histological studies show in furosemide groups vacuolar degeneration in the Cardiac muscle fibers, with the loss of nuclei in most of those fibers, white blood cell proliferation was found in most of the heart tissue, the coronary blood vessels contained decomposing blood, and most of fibers are hypertrophied and compact with each other in the form of a single mass. It also appeared that there was hypothesis of hypertrophy of the cardiac muscle fibers and the spread of wide vacuoles in the cytoplasm of these fibers. Some of the muscle fibers lost their nuclei and the coronary. Conclusions: We conclude from the results of our current study that furosemide has a clear effect on the studied parameters, especially the heart and kidneys, in the various doses given and according to the time period of the study.
