Final answer:
The heart is made of cardiac muscle. The muscles that line the gut and veins/arteries are smooth muscles. Both cardiac muscle and smooth muscle are involuntary.
Step-by-step explanation:
The heart is made up of cardiac muscle. The muscles that line the gut are called smooth muscles, while the muscles that line veins and arteries are called smooth muscles as well. Cardiac muscle and smooth muscle are both examples of involuntary muscles.