RB-82 IS ANALOGOUS TO POTASSIUM ION (K+) IN ITS BIOCHEMICAL BEHAVIOR AND IS RAPIDLY EXTRACTED BY THE MYOCARDIUM PROPORTIONAL TO THE BLOOD FLOW. RB+ PARTICIPATES IN THE SODIUM-POTASSIUM (NA+/K+) ION EXCHANGE PUMPS THAT ARE PRESENT IN CELL MEMBRANES. THE INTRACELLULAR UPTAKE OF RB-82 REQUIRES MAINTENANCE OF IONIC GRADIENT ACROSS CELL MEMBRANES. RB-82 RADIOACTIVITY IS INCREASED IN VIABLE MYOCARDIUM REFLECTING INTRACELLULAR RETENTION, WHILE THE TRACER IS CLEARED RAPIDLY FROM NECROTIC OR INFARCTED TISSUE.