It may be difficult to determine the cause of dilated cardiomyopathy. However, many things can cause the left ventricle to dilate and weaken, including: Certain infections Complications of late-stage pregnancy Diabetes Excessive iron in the heart and other organs (hemochromatosis) Heart rhythm problems (arrhythmias) High blood pressure (hypertension) Obesity Heart valve disease, such as mitral valve or aortic valve regurgitation