The story of coronary artery disease (CAD) begins with where artery blockages occur and where they don't. Typically, blockages occur in the coronary arteries on the outer surface of the heart. However, blockages are not often found in arteries or veins in any other part of the body (though carotid blockages are becoming more common). Furthermore, the CAD blockages do not naturally occur in other species. What's different about the coronary arteries of the human species that make them vulnerable to heart disease?
To explain the difference, Linus Pauling posited a theory, his Unified Theory of Heart Disease. Pauling observed that the CAD blockages occur in areas of high mechanical stress. Due to their location, these arteries are subject to continuous squeezing, pulling, and tugging from the ceaseless contractions of the heart. Like a garden hose that's repeatedly compressed or squeezed, this mechanical stress has the potential for causing damage. Normally, the body quickly repairs that damage, and in most other mammals (those that do not naturally suffer from CAD), the repair is seamless. In humans, however, the repeated repair process leads to CAD. Why?