Type of carbohydrate is a vital emergency fuel for heart muscle

glycogen is vital emergency fuel for heart. glycogen is a polymer of glucose that is a storage form carbohydrate in animals. it synthesized from the excess glucose by the enzyme glycogen synthase and stored in hepatocytes and cardiomyocytes. in case of angina attack in the heart glycogen stored in cardiac muscle helps the heart to survive for a duration of about 40-60 seconds.    

Glycogen is a vital emergency fuel for heart muscle. Glycogen acts as an energy source for the body. If your body has extra glucose it is stored in the liver or muscles, so that it can be used at another time. Glycogen stores glucose and both humans and other animals have it.

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.