A cardiac shunt would be best demonstrated with which nuclear medicine technique?

First pass radionuclide angiography is particularly effective for demonstrating a cardiac shunt due to its ability to capture the rapid passage of a radioactive tracer through the heart and major vessels in real time. This technique involves injecting a bolus of radiopharmaceutical, which allows for immediate visualization of the blood flow dynamics and any abnormal pathways, such as shunts. Since cardiac shunts can lead to abnormal mixing of oxygenated and deoxygenated blood, first pass radionuclide angiography is well-suited to detect these discrepancies, providing a clear assessment of the efficiency of the heart's blood flow during its initial phases.

In contrast, equilibrium-gated ventriculography primarily focuses on the assessment of ventricular function and wall motion over a longer period, which may not sufficiently highlight rapid flow abnormalities. Myocardial infarct imaging is designed to evaluate areas of the heart that have been damaged by ischemia, while myocardial perfusion imaging helps to assess blood flow to the myocardium but may not provide the rapid temporal resolution needed to clearly identify shunt presence. Hence, although these techniques are useful in their respective contexts, they do not offer the same immediate insight into shunting as first pass radionuclide angiography does.