In complex therapy of acute or chronic cardiac failure, the use of valve-free centrifugal pumps or artificial heart ventricles takes place. In these cases, simultaneous monitoring of cardiac and pump performance is very important. In this study, an ultrasound dilution method based on the registration of two dilution curves after intravenous injection of isotonic and hypertonic sodium solution was developed. Comparison of total cardiac output (TCO), which included pump and heart output measured by thermodilution and ultrasound (TCOus) dilution, yielded TCOus = 1.11TCOth - 0.54 (n = 13).