Type 2 diabetes physically changes the human heart. A study of donated human hearts found that diabetes disrupts the way heart cells produce energy. It weakens the muscular structure of the heart. It triggers a buildup of tough fibrous tissue, making it harder for the heart to pump. These changes are particularly severe in people with coronary heart disease. Ischemic heart disease is the most common cause of heart failure. Type 2 diabetes also increases the risk of heart disease.