Effect of hemodilution on capillary and arteriolovenous shunt flow in organs after cardiac arrest in dogs. The purpose of this study was to observe the changes in capillary and arteriolovenous shunting blood flow after cardiac arrest and subsequent resuscitation by venous return occlusion produced by inflation of an intra-atrial balloon and cross-clamping of the ascending aorta, and to determine how hemodilution might modify such changes. Organ capillary blood flow and the fractional distribution of cardiac output were measured by the microsphere (9-microns diameter) trapping method in dogs. Simultaneously, the arteriolovenous shunt rate was measured by continuous collection of venous blood drained at 4.8 ml.min-1 for 2 min from the brain, kidney, liver, splanchnic organs, skeletal muscle of the pelvic limb, and all of the systemic circulatory organs. The capillary blood flow of the brain, thyroid gland, pancreas, and stomach decreased after circulatory arrest in five nonhemodiluted dogs (group C); arteriolovenous shunt rate was unchanged after circulatory arrest in this group. However, with hemodilution, which was induced either before (pre group, n = 5) or after (post group, n = 5) circulatory arrest, no change occurred in the shunt rate in any of the organs, with the exception of an increase in the systemic arteriolovenous shunt rate in the pre group. Capillary blood flow was maintained at almost the same level as before circulatory arrest in the pre group, but increased significantly in several organs of the post group. The data indicated that hemodilution might be effective for prevention of organ ischemia after cardiac arrest. 