We propose to measure coronary blood flow in patients with acute myocardial infarction and patients with angina pectoris, before and during acute interventions. Myocardial blood flow (expressed as ml/100 g LV/min) will be measured using an inert gas washout technique, with argon as indicator. Coronary sinus blood flow (expressed as ml/min) will be measured by an indicator dilution technique, using neon as indicator. The measurements will be performed using a newly-developed coronary sinus catheter and blood gas analysis will be by a mass spectrometer technique. Both determinations will be performed in the same individual in close time sequence. The washout curves will be analyzed with the heart treated arbitrarily as a 2-compartment model, and "fast" and "slow" perfusion areas will be identified and quantitated (expressed as grams of LV). Myocardial blood flow and coronary sinus blood flow data will then be combined to yield information regarding the size of ischemic areas. Using these techniques, the effect of interventions such as nitroprusside and intra-aortic balloon pumping on the relative size of ischemic areas can be evaluated. This approach should yield information regarding the effects of interventions on the mycardium of patients with acute myocardial infarction not readily available by other techniques.