Abstract: A thermodilution injectate assembly which includes a length of flexible tubing for introducing fluid from a solution container to the assembly. An insulated container which holds a heat exchange medium and into which is positioned a substantially flat plate heat exchanger. The heat exchanger includes an inlet port and an outlet port and a fluid-flow path therebetween, which path provides a heat exchange relationship between fluid flowing through the path and the heat exchange medium. A dual directional valve is connected to the outlet port of the heat exchanger and to the solution container. A three-ported stopcock is in fluid-flow communication with the dual directional valve. A syringe is connected to a port on the three-ported stopcock and a length of flexible tubing is connected to a port on the three-ported stopcock for delivering the cooled fluid to a patient for monitoring the cardiac output.