A fetal heart rate tracing with absent variation and a sinusoidal pattern led to the diagnosis of acute fetomaternal hemorrhage at 29 + 2 weeks' gestation. The middle cerebral artery had increased peak blood flow velocity with reversed end-diastolic flow. Fetal coronary arteries visualized by color-coded and pulsed wave Doppler sonography showed slight decrease of time-averaged maximum velocities after oxygen administration, while cerebral flows remained unchanged. After administration of 50 ml blood (pre-transfusion hematocrit < 11%) the middle cerebral artery flow normalized and coronary artery velocities decreased further until coronary blood flow could no longer be visualized within 30 min of the transfusion (post-transfusion hematocrit 27%). Evidence of successful fetal resuscitation also included normalization of the fetal heart rate tracing and resumption of fetal activity (biophysical profile score 8/10). This was also observed after a second transfusion of 38 ml blood. Deterioration from repeated fetomaternal hemorrhage led to delivery of a severely anemic neonate (cord hematocrit 7%) by Cesarean section. Postnatally, a single seizure, moderate severity respiratory distress syndrome and grade III intraventricular hemorrhage were noted. Increased peak blood flow velocity with reversed end-diastolic flow may be observed in the middle cerebral artery of fetuses with acute anemia. Correction of this phenomenon with transfusion suggests that hypovolemia and low blood viscosity are major contributing factors. Furthermore, decreasing coronary artery blood flow velocities with supplemental oxygen and blood replacement confirm functional autoregulation of the fetal coronary circulation. Observation of these acute flow changes during fetal surveillance warrants investigation for a potentially serious underlying condition.