A large quantity of glycogen is beneficial only under ischemic conditions. Glycogen accumulation in the myocardium favours the incidence of pre-excitation syndrome. Several studies have reported an association of the EDs and/or alcohol with the occurrence of negative effects at the cardiovascular level 2therefore, we cannot exclude the possibility that these effects were connected to glycogen accumulation in the myocardium. Born errors of carbohydrate metabolism covered in this include disaccharidase deficiencies, disorders of monosaccharide metabolism, glycogen storage diseases, and gluconeogenic disorders. This chapter focuses mainly on clinical aspects, genetics and current treatments for these disorders. The defective digestion of dietary disaccharides starch, lactose and sucrose is due to deficiencies of congenital lactase, adult-type lactase, or sucrase-isomaltose. Disorders of monosaccharide metabolism include defects in transport enzymes of galactose metabolism enzymes of fructose metabolism and dehydrogenases of pentose metabolism To date, there are over 12 glycogenosis, or glycogen metabolism disorders, that have been catalogued. Glycogen storage diseases (GSD), a major category of glycogenosis, are categorized by the type of tissue involved: liver, muscle, and/or cardiac. Gluconeogenic disorders entail deficiencies of fructose-1,6-diphosphatase, pyruvate carboxylase, phosphoenolpyruvate carboxin’s, and pyruvate dehydrogenase complex.