The effects of acute myocardial ischemia produced by coronary artery occlusion on left ventricular (LV) dynamics will be studied in intact conscious dogs. Animals will be instrumented for measurements and radio telemetry of: 1) overall LV function with LV miniature pressure gauges for LV systolic and diastolic pressure, dP/dt and dP/dt/P and endocardial dimension transducers for LV diameter and dD/dt, i.e., velocity of myocardial fiber shortening and aortic electromagnetic flow probes for stroke volume and cardiac output; 2) regional LV function with multiple pairs of miniature ultrasonic crystals implanted in the LV for regional segment length and regional velocity of myocardial fiber shortening in normal, border, and ischemic zones along with a miniature LV pressure gauge. All animals will have flow probes on either the left circumflex and/or anterior descending coronary arteries. Coronary flow will be reduced in the left main, left anterior descending or left circumflex coronary arteries by inflation of implanted hydraulic occluders. Overall LV function as well as function of specific regions, which may be normally perfused, ischemic or in the border zone, will be correlated with: 1) a measure of myocardial damage as indicated by intramyocardial EKG mapping, CPK determination and histology; and 2) regional myocardial blood flow determined by the microsphere technique. These studies in conscious dogs will include reduction of coronary blood flow resulting in global or regional myocardial ischemia and prolonged regional myocardial ischemia resulting in myocardial infarction. Both overall and regional LV function will be correlated with the above mentioned indices of myocardial ischemia and with measurements of regional myocardial perfusion in response to interventions that: 1) alter myocardial oxygen consumption; 2) protect the ischemic myocardium; and 3) constrict coronary vessels under normal circumstances.