Cardiovascular complications are one of the major causes of death in diabetes mellitus. Piper sarmentosum (P.s) is an herb that possesses antihyperglycaemic effects. The main aim of the study was to observe the histological changes in the heart and the proximal aorta of streptozotocin-induced diabetic rats following P.s administration. Twenty-four male Sprague-Dawley rats (n=24) were equally randomized into four groups: control group supplemented with normal saline (C); control group supplemented with P.s (CTx) ; diabetic group supplemented with normal saline (D) and, diabetic group supplemented with P.s (DTx). Diabetes was induced by STZ (50mg/kg body weight) intramuscularly. P.s extract (0.125g/kg) was administered orally for 28 days, following four weeks of STZ induction. The cardiac and aortic tissues were collected and processed under different stains: Haematoxylin and Eosin (H & E), Verhoeff-Van Gieson (VVG), Masson’s Trichome (MT) and Periodic Acid- Schiff (PAS). There were abnormal cardiomyocytes nuclei, disarray of myofibres and increase in connective tissue deposits in cardiac tissues of the diabetic untreated group. The thickness of tunica media and ratio of tunica intima to media were found to be significantly increased in the aorta of diabetic untreated group (P < 0.05) compared to the control group. There were
degenerative changes in the proximal aorta in diabetic untreated groups. All the histological damages of cardiac and aortic tissues were found to be lesser in the diabetic treated groups. Supplementation with P.s extract prevented the oxidative damage arising from diabetes mellitus, and reduced its complications.