Cardiolipin (bisphosphatidyl glycerol) is an important component of the inner mitochondrial membrane, where it constitutes about 20% of the total lipid. It is typically present in metabolically active cells of the heart and skeletal muscle. It has also been observed in certain bacterial membranes.

This is a phospholipid. Some individuals make an antibody to cardiolipin and this causes the blood to clot too quickly. Patients who lose pregnancies through miscarriage sometimes have a false positive test for syphilis because they have antibodies to cardiolipin that were manufactured when the pregnancy miscarried.