QUOTE: "what is the difference in cardiomyopathy and cardiomegaly?"
>>>>>>Literally both terms mean an enlarged heart. Sometimes cardiomegaly indicates a mildy enlarged heart that is not pathological such as an athlete's heart.
Cardiomyopathy is an enlargement that is patholgically based and secondary to inflammation of the heart muscles. Cardiomyopathy can be caused by a variety of heart problems or by a viral infection, and when the heart muscles become inflamed, there is a loss of contractility and grow weaker, resulting in faster heart rate and a harder working heart to circulate blood into the circulator system. Harder working heart enlarges the left ventrical.
Hypertrophic cardiomyopathy is a form of cardiomyopathy in which the walls of the heart's chambers thicken abnormally. This condition causes less blood to fill the heart chamber because the walls do not relax and are stiffer than normal. Also, the enlargement of the walls can reduce the space available to be filled.
Dilated cardiomypathy is an increase in the internal dimension of the left ventricle's chamber. The walls can be thicker than normal as well. Dilated cardiomyopthy can result from a valve opening that is too narrow and that develops intra-chamber pressure that can dilate the ventricle either left or right ventricle, etc. The heart's LV normally dilates to help maintain a balance of blood flow between the right and left side. When the LV dilates within an acceptable range there is increased contractility, and if the dilatation overcompensates outside the acceptable range due to heart issue the contractility decreases...as analogy when a hand spring is stretched the spring responds with a stronger recoil...if over stretched it becomes flaccid..explained by the Frank/Starling law of physics.
Hope this gives you a persepctive, and if you have any further questions you are welcome to respond. Thanks for the question, take care.