Type 1 diabetes patients are insulin deficient resulting in hyperglycaemia. Diabetic patients have a higher risk of cardiovascular diseases. In this study the progression of cardiac metabolic and functional decline was followed in a streptozotocin (STZ) induced Type 1 diabetic model. Flux through pyruvate dehydrogenase was significantly decreased at 2 and 6 weeks post STZ injection. Interestingly, the incorporation of the 13C-label from pyruvate into lactate and alanine was decreased at 2 weeks, but significantly increased at 6 weeks. Cardiac output was normalized after 6 weeks. Such studies will allow a better understanding of the interactions between metabolism and function in the diabetic heart.