NADH is the Nicotinamide adenine dinucleotide e FADH2 is the Flavin adenine nucleotide, both of them are high energy electron carriers. They are reponsible for transporting electrons generated in Glycolises and Krebs Cycle to the Electron Transport Chain, creating ATP.The difference between them is that a NADH molecule produces 3 ATP molecules while a FADH2 molecule produces 2 ATP molecules.