A study in The Journal of the American College of Cardiology" suggests a possible reason. Obesity leads to changes in how the heart works.
After comparing the hearts of more than 900 people, researchers found those severely overweight had impaired functioning of the left ventricle. It's one of the four chambers of the heart. That means oxygen rich blood is not being pumped normally.
The dysfunction may explain the increase risk of heart failure in those with excess body weight.