1. A technique used for measuring the size of a fluid-filled cavity by injecting a very cold sample of known volume and by measuring the change in temperature of the whole, assessing the degree of thermodilution, and hence the total volume of the cavity.
2. A method of cardiac output determination.

A bolus (intravenous injection of a solution) of known volume and temperature is injected into the right atrium, and the resultant change in blood temperature is detected by a thermistor previously placed in the pulmonary artery with a catheter.