The fruit fly Drosophila melanogaster has served as a valuable model- organism for the study of aging and was the first organism possessing a circulatory system to have its genome completely sequenced. Little is known however about the function of the heart-like organ of flies during the aging process. We have developed methods for studying cardiac function in vivo in adult flies. Using two different cardiovascular stress methods (elevated ambient temperature and external electrical pacing) we found that maximal heart rate is significantly and reproducibly reduced with aging in Drosophila, analogous to observations in elderly humans. We have also described for the first time several other aspects of the cardiac physiology of young adult and aging Drosophila, including an age- associated increase in rhythm disturbances. We propose that the study of declining cardiac function in aging flies may serve as a genetically tractable model for genome-wide mutational screening for genes that protect against cardiac aging. Our specific aim is to identify at least one gene that can retard the age- related decline in cardiac function in Drosophila. Our long-term aims are to obtain a complete picture of the genetics of cardiac aging in Drosophila and to use this to stimulate investigations in vertebrates.