The document summarizes analytical techniques for investigating the spatial distribution of copper and iron in cardiac tissue, including electron probe microanalysis, secondary ion mass spectrometry, and nuclear microscopy. Electron probe microanalysis can detect elements at the 100 ppm level with 1 μm resolution but lacks sensitivity. Secondary ion mass spectrometry has ppb-ppm detection limits at 1 μm resolution but provides non-quantitative analysis of biological samples. Nuclear microscopy can determine spatial distribution of metals in biological tissue if prepared properly, using techniques like Rutherford backscattering spectroscopy, scanning transmission ion microscopy, and particle induced x-ray emission.