The reliable and safe production of myocardial infarction in closed-chest animals is of paramount research interest. To date, the injection of particulate matter and the introduction of occlusive solid plugs have been described. Because of the limited size of the catheter, only small branches could be occluded, which resulted in a high incidence of mortality. A new simple technique is described that allows occlusion of a major coronary artery at a preselected site. An Ivalon (polyvinyl alcohol) plug compressed around the tip of an introducing wire is advanced through a selectively placed catheter into the coronary artery. It is felt in place for 5 minutes and assumes its original size upon contact with blood. Once the plug is re-expanded, the wire is withdrawn. The new technique was carried out successfully on nine dogs with no immediate fatality and myocardial infarction as demonstrated by cine ventriculography and histopathologic examination.