The time relationships of aortic blood flow and other hemodynamic variables were measured prior to, during, and after myocardial infarction in the dog. A helical magnesium wire placed in the coronary artery produced gradual occlusion with infarction in approximately ten days. Serial measurements of hemodynamic data showed significant changes during the time of infarction with return to preinfarction levels within three days. The heart rate increased 87 and the mean blood pressure decreased 10% without significant arrhythmia during infarction. The aortic flow, velocity and mean acceleration of flow decreased 8, 16, and 23% respectively, while the pre-ejection period did not change significantly. These findings suggest that the hemodynamic changes during myocardial infarction are the result of altered myocardial function. The measurements of electrical and mechanical time relationships are sensitive indicators of cardiac performance in myocardial infarction.