Hemorrheology was studied in patients undergoing artificial heart support as a bridge-to-cardiac transplantation. Abnormal hemorrheology was seen in two patients, one on a Jarvik-7 total artificial heart, and the other on a Novacor left ventricular assist device. Both of these patients suffered neurologic episodes. The rheology of these two patients coincided well with their clinical status, and was accompanied by marked increases in relative blood viscosity, erythrocyte rigidity, fibrinogen concentration, and platelet aggregation. Results show that improving hemorrheology may be a beneficial avenue to pursue in preventing or treating transient ischemic attacks or other complications in patients during support with mechanical devices.