A new method of measuring the cardiac output is disclosed. The new method uses an ultrasound emitter and one or more receivers placed in the superior vena cava just above the right atrium of the heart so that the ultrasound apparatus can transmit through the wall of the superior vena cava and the juxtaposed wall of the aorta at this location. By measuring the velocity of the blood by its back-scattered Doppler shift, the cardiac output can be determined. The volume of blood flow can also be determined by measuring the diameter of the aorta.
