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A retrograde coronary vein injection technique for concentrating radioisotope in ischemic myocardial regions was evaluated in dogs. Potassium-43 in saline solution was injected into the coronary veins during complete closure of the coronary sinus. In the presence of coronary inflow obstruction, the venous potassium-43 was distributed mainly to the low pressure vessels in ischemic heart regions; i.e., the ratio of potassium-43 in the occluded-to-unoccluded areas ranged from 2:1 to 3:1 thirty seconds after retrograde injections. Krypton-85 in saline solution was injected under pressure into the coronary veins during partial closure of the coronary sinus. In the presence of inflow obstruction, the ratio of krypton-85 in the occluded- to-unoccluded areas ranged from 4:1 to 6:1 sixty seconds after retrograde injections; larger ratios may be expected after rapid washout of gas from the normally perfused region is nearly complete. Myocardial potassium-43 imaging techniques were applied to locate and measure the size of the ischemic heart region as a radioisotopic hot spot. Detection of hypoperfused areas of extremely small size may be accomplished by this technique.

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