Chronic hyperglycaemia (HG) induced by diabetes mellitus (DM) is known to elicit adverse structural remodelling in the heart. This study investigated the impact of age-induced hyperglycaemia (2 and 4 months) on structural remodelling in the left ventricle (LV) of the streptozotocin (STZ)-induced type 1 diabetic (T1DM) rats compared to age-matched Wistar controls. The study measured the general characteristics of the animals, structural changes, fibrosis, apoptosis and gene expressions for extracellular matrix (ECM) factors, transforming growth factor beta 1 (TGF-beta1), brain natriuretic peptide (BNP), atrial natriuretic factor (ANP) and calcium transporting proteins using immune-histochemical, immunoblotting and quantitative gene expression analysis. The project had the relevant ethical clearance from each institution to undertake the study. The results revealed that STZ-induced diabetic rats weighed significantly (Student’s t-test; p<0.01) less than their age-matched controls and these reductions in weight were more severe with increasing age (270±5.78** vs. 343±9.99) at 2 months and (221±13.02**vs. 378±10.63) at 4 months post STZ-treatment. Similarly, heart weights were also significantly (p<0.01) lower along with an increase in the HW/BW ratio at 2 and 4 months indicating signs of hypertrophy. Plasma blood glucose levels were significantly elevated in T1DM animals after 2 months (443±12.2** vs. 98±3.79) and 4 months (446±18.8** vs. 97±3.04) of treatment. Cell viability measured by the percentage (%) of viable myocytes was significantly decreased (p<0.01) at 2 months (46.2±7.5% vs. 69.0±5.8%) and at 4 months (29.5±1.2% vs. 51.4±3.5%) in LV form STZ-treated rats compared to age-matched controls. These changes were accompanied by structural alteration of the heart and also by significant (p<0.05) increases in fibrosis, apoptosis and gene expressions for BNP, ANP, TGF-beta 1, ECM factors and their regulators, and calcium transporting proteins in the LV of rats induced with TIDM for 2 and 4 months compared to the respective Wistar controls. These results reveal that age-induced hyperglycaemia can evoke profound adverse remodelling of the LV with more severity at 4 months of TIDM.