In order to limit the hemodilution effect during cardiopulmonary bypass (CPB) in low weight animal patients, blood is often used as a component of the prime solution. This study was undertaken to evaluate the effects of the addition of blood to the prime solution on the hemodynamic and respiratory parameters during and following mitral valve replacement in dogs. Ten dogs were randomly assigned to receive either a hemic (HP), 75% blood component, or a nonhemic prime (NP) solution. The hemodilution was 5 +/- 4% and 25 +/- 10% for the HP and NP groups, respectively. Cardiopulmonary measurements were taken 20 minutes before initiating CPB, during CPB, and 20 min after termination. The hematocrit level, the hemoglobin concentration, and the arterial oxygen content were significantly lower in the NP group during and following CPB. However, the systemic oxygen transport index was not significantly different between the NP group (355 +/- 87 mL/min/m2) and the HP group (546 +/- 155 mL/min/m2) following CPB. Our study indicates that, in normal dogs undergoing hemodilution from a nonhemic prime solution, the cardiovascular function is able to maintain the systemic oxygen transport in the period immediately following mitral valve replacement.