Abstract: Macroaggregated serum albumin (MAA) particles labeled with 131iodine (131I) or similar particles-labeled with 99mtechnetium (99mTc) or both types were injected directly into the coronary circulation of 29 patients at the time of conventional coronary arteriography. Radionuclide images of the distribution of these small (10-60 µ) biodegradable particles in the small vessels of the heart wall were made with a commercial Anger-type scintillation camera in much the same way as routine pulmonary perfusion scans are made. The resulting images depicted the relative regional distribution of blood flow to the myocardium in these patients suspected of having coronary artery disease. The myocardial perfusion images were of good quality and allowed gross assessment of perfusion by way of each major coronary artery. This was done by injecting 99mTc-labeled particles into the left coronary artery and 131I-MAA into the right coronary artery through the coronary artery catheter. Separate or composite images of the relati...