Background. Inflammatory genes may be unevenly expressed in different heart chambers. Methods. Biopsies were taken simultaneously from the right atrium (RA), left atrium (LA), and left ventricle (LV) of 19 patients before cardioplegic arrest during open heart surgery. The mRNA expression of tumor necrosis factor alpha (TNF alpha), interleukin 1 beta (IL-1 beta), inducible and endothelial nitric oxide synthase (iNOS and eNOS), endothelin-l (ET-1), E-selectin (CD62E), intercellular adhesion molecule-1 (ICAM-1) and its ligand CD18, and CD25 was evaluated with semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Results. Expression of TNF alpha mRNA was higher in RA than LA and LV (p < 0.05), whereas IL-1 beta was more expressed in LA than RA (p < 0.05), which was higher than LV (p < 0.0001). There were no significant regional differences in the expression of ICAM-1, CD62E, CD25, iNOS, and eNOS. CD18 was higher in RA than LA (p < 0.05); ET-1 was more expressed in RA than LV (p < 0.04). Patients with stable angina had no expression of eNOS. Conclusions. Gene expression of inflammatory mediators was detected in the hearts of patients with different cardiovascular disorders, and was unevenly distributed in different heart chambers. Cardiac biopsies should be taken from the same site. (C) 2000 by The Society of Thoracic Surgeons.