Objectives: The effects of anemia of prematurity during bronchopulmonary dysplasia (BPD) as well as on the metabolic and erythropoietic functions were determined before and after a transfusion. Fourteen anemic (Hb range: 65-88 gm/L), oxygen dependent (fraction of inspired oxygen ≤35%), nonventilated, preterm infants with BPD were studied at a postnatal age of 6 ± 2 weeks. Study Design: Cardiac output, heart rate, mean velocity of circumferential fiber shortening, shortening fraction (SF), and stroke volume were assessed by pulsed and continuous wave Doppler echocardiography. Values for resting oxygen consumption, carbon dioxide production, and energy expenditure were obtained by indirect calorimetry. The affinity of oxygenated hemoglobin was determined by a blood oxygen dissociation analyzer. Results: An increased hemoglobin level resulted in auppression of erythropoietin secretion (p < 0.001), whereas heart rate, cardiac output, stroke volume, and SF decreased (p < 0.05). Weight gain before and after transfusion were similar. Plasma lactate levels decreased from 1.6 ± 0.3 to 1.2 ± 0.3. Oxygen consumption, carbon dioxide production, and energy expenditure were not affected. Conclusions: Anemia of prematurity and BPD increase heart rate, cardiac output, stroke volume, and SF. These hemodynamic compensatory responses are normalized by transfusion. (J Pediatr 1998;132:630-4.)