Endocardial (EE) and Aortic (AE) endothelial cells were isolated from the same two rats, pooled (EE and AE kept separately) and cultured for 2 passages. Culture conditions and confluence of EE and AE cell cultures were kept as identical as possible. RNA was isolated and the expression profile of both endothelial cell types was compared using the Affymetrix rat genome U34A array.