In order to examine the effects of chronic low G acceleration on blood flow distribution and cardiac output, chickens (N=10) were centrifuged at +2Gz for 30-61 d. Controls (N=12) were not centrifuged. The animals were anesthetized with sodium pentobarbital after removal from the centrifuge and surgically prepared in order to measure cardiac output and regional blood flows by the reference sample method with 85Sr labeled microspheres (15 +/- 5 mum diam.). Both brachial arteries were cannulated to withdraw timed, paired blood samples at a known rate. The chest was opened and a cannula inserted into the left ventricle for administration of microspheres. Tissue samples were taken after completion of experimental procedures and their radioactivity was determined. The cardiac outputs in the two groups were not significantly different. Regional blood flows to the kidney, eyes, and skeletal muscle were significantly increased in the animals subjected to chronic +2Gz. While the mechanism by which these increases in blood flow occurred is not known, results indicate that chronic exposure to hyperdynamic gravitational fields can alter circulatory dynamics. We conclude that the cardiovascular system is directly involved in the process of adaptation to chronic positive acceleration.