The present invention provides a rapid, economical test for the detection of a right to left shunt applicable to the population at large due to its safety and noninvasiveness. The intended procedure involves gaining access to the circulatory system, injecting a measurable substance, ideally during prolonged and/or repeated Valsalva maneuvers, and then rapidly and repeatedly, ideally continuously, assaying for the substance. Through the determination of the appearance of a small amount of the substance prior to the subsequent high concentrations generated by the remainder of the bolus, one may safely diagnose a meaningful communication between the right and left heart, or other right to left shunt bypassing the lungs.
