The leading cause of death for people suffering from type 2 diabetes is heart disease. The ability of the diabetic heart to pump blood around the body is diminished. Despite many decades of research, the underlying cause for the weakening of the diabetic heart is not well-understood. We propose that a reduction in the capacity to supply energy to sustain the diabetic heart is the main reason for the decline in its performance. We will test our hypothesis by measuring the energetic and mechanical properties of human heart tissues from type 2 diabetic patients. The data will be interpreted using a mathematical model of energy balance in a heart cell. Our findings have the potential to uncover why the diabetic heart becomes compromised and identify new treatment approaches to improve the health of diabetic patients.