Primary cultures of newborn rat cardiomyocytes were grown in medium supplemented with cyclic fatty acid monomers (CFAM) which had been isolated from heated linseed oil. The cells were harvested, and lipids were extracted and fractionated using silica cartridges and high-performance liquid chromatography. The CFAM structures isolated from cellular lipids were determined and compared to those that had been supplemented to the medium, using gas-liquid chromatography coupled with mass spectrometry (GC/MS). We found that CFAM were incorporated into phospholipids and neutral lipids of cardiomyocytes. Furthermore, CFAM with a cyclopentyl ring structure were more abundant in cardiomyocytes than were the cyclohexyl ring isomers. Our data suggest that CFAM of the 5-carbon and 6-carbon ring series are metabolized differently in newborn rat cardiomyocytes.