What happens to any person right after eating, especially if it's a heavy meal, is that the body is focusing 100% on digesting that food. That's why the body temperature can lower and fatigue
is common. When someone has a heart disease
, that person is already easily tired because of the heart that is unable to pump out blood in a normal fashion, maybe the heart needs to pump faster or harder, depending of the type of disease and other conditions of the person (like obesity). Hope this helps to clarify a bit.