A multienzyme complex possessing three activities in two subunits (alpha and beta) that catalyzes three steps of the fatty acid beta-oxidation cycle within the mitochondrial matrix. The alpha subunit comprises the enoyl-CoA hydratase (ECH) and 3-hydroxyacyl-CoA dehydrogenase (HACD) activities, and the beta subunit contains the acetyl-CoA C-acyltransferase (KACT)/thiolase activity. [ GOC:sjm http://www.ncbi.nlm.nih.gov/pubmed/29915090 ]