A new method for cardiovascular shunt detection is described using the indicator-dilution principle applied to blood conductivity changes produced by 5 per cent saline. It possesses these distinct advantages over the Evans blue technic: (1) an unlimited number of determinations can be made without an increasing blood dye background or bluish discoloration of the patient, (2) oximetric determination of blood oxygen saturation is not interferred with, and (3) a simple modification of the carrier amplifiers of commonly used recording systems supplies most of the necessary instrumentation.