['Recent studies demonstrated that cultured primary cardiomyocytes are a valuable tool for studying the metabolic capacity of the heart. However, a major limitation for isolated cardiomyocytes is that they are rather fragile and difficult to isolate. Therefore, there is an urgent need for an in vitro cell line model.', 'Expression of different cytochrome P450 (CYP) genes were examined in a rat H9c2 cell line in comparison with that of rat heart. RNAs from H9c2 cells, rat heart as well as rat liver were isolated and CYP mRNA expression was determined by reverse transcription-polymerase chain reaction.', 'Our results showed that CYP1A1 and 1B1 are constitutively expressed in both H9c2 cells and the heart. CYP1A1 was induced by beta-naphthoflavone in H9c2 cells and the heart, whereas CYP1B1 was only induced in the heart. CYP2B1, 2B2, 2E1 and 2J3 were expressed in H9c2 cells and the heart at a comparable level but significantly lower than that detected in the liver. Expression of CYP2C11, 2C13, and 2C23 appeared to be greater in the cell line than in heart. On the other hand, CYP2A1, 3A1, and 3A2 were not expressed either in H9c2 cells or in the heart.'] Is h9c2 cell line a valuable in vitro model to study the drug metabolizing enzymes in the heart?