There is cardiac dysfunction in male eNOS (-/-) with age and 50% mortality at 21M. It was of interest to investigate the gene expression profile of aged eNOS (-/-) male in comparison to (+/+) in order to explore the genetic markers and molecular mechanisms leading to heart failure. RNA was extracted from the left ventricle from male (-/-) (n=3) and (+/+) (n=4) at the age of 21M. Keywords = eNOS knockout Keywords = microarray Keywords = exercise