Once inside the mitochondria, each cycle of β-oxidation, liberating a two carbon unit (acetyl-CoA), occurs in a sequence of four reactions:
This process continues until the entire chain is cleaved into acetyl CoA units. The final cycle produces two separate acetyl CoAs, instead of one acyl CoA and one acetyl CoA.  For every cycle, the Acyl CoA unit is shortened by two carbon atoms. Concomitantly, one molecule of FADH, NADH and acetyl CoA are formed.