A digital simulation of the cardiovascular and pulmonary systems of a newborn infant was developed and tested. More specifically, the model was designed to emulate the blood gas chemistry of the neonate and it's effect on respiratory stimulus, cardiac output and Ductus Arteriosus shunting. Pulmonary and cardiac system dynamics were not considered in the simulation. The model underwent a series of tests in which controlled mockups of actual physiological conditions were simulated. The effect of metabolic rate changes, Ductus Arteriosus shunting, and alveolar membrane disease on the pulmonary and cardiovascular systems was studied in steady state conditions. The dynamic alterations in the neonatal system due to respirator therapy and carbon dioxide inhalation was investigated. Finally, a simulation of an actual clinical case was undertaken. While the model worked well in the controlled environment tests, it showed some deficiencies in the clinical case study. Additional clinical data is needed to improve the respiratory and cardiac control mechanisms in the simulation. Further, a more complete blood buffer system needs to be incorporated into the model. / M.S.