Detection and quantitation of shunts can be done accurately, rapidly, and safely using radionuclide techniques. The most frequent use of radionuclides in the evaluation of shunts is first-pass radionuclide angiography for the detection and quantitation of left-to-right shunts. Thallium-201 myocardial scintigraphy is useful in the evaluation of right ventricular overload secondary to left-to-right shunting. Radionuclide angiography has applications for premature and newborn infants with patent ductus arteriosus and respiratory distress, older children with unexplained heart murmur, and in the postoperative evaluation of patients undergoing cardiovascular surgery.