L Carnitine Supplement: Heart Concerns Advanced Molecular Labs Keep your dog's heart strong and healthy! As dogs age, heart disease can become a common challengebut with the right support, you can help improve their quality of life. Metabolic therapy for cardiovascular diseases with propionyl L carnitine ScienceDirect Mitochondrial control of fuel switching via carnitine biosynthesis Science L carnitine is primarily synthesized in the liver from the amino acids lysine and methionine through a series of four enzymatic reactions, with the liver and kidneys converting the precursor butyrobetaine into active