A B S T R A C T Coronary flow, left ventricular circumference, and left ventricular pressure were observed in the isovolumically contracting, isolated canine heart supported with arterial blood from a donor. Systolic pressure, heart rate, and coronary perfusion pressure were held constant while the coronary bed was progressively embolized with either large (average 865 A) or small (average 10 /A) polystyrene microspheres. During embolization with large microspheres, coronary flow diminished progressively. After sufficient embolization, decreased ventricular performance was indicated by a rise in end-diastolic pressure. During embolization with small microspheres, coronary flow initially increased, which suggests the effective release of a vasodilator substance. Return of coronary flow to control levels occurred only after the end-diastolic pressure rose, on the average, to above 30 mm Hg. After embolization with both sizes of microspheres, ventricular diastolic pressure-v6lume relationships showed decreased ventricular compliance. This was attributed, in part, to edema of the ventricular wall and, in part, to focal shortening of the sarcomeres where the circulation was compromised. Embolization with both sizes of microspheres ultimately caused a decrease in ventricular performance, although when the systolic pressure was increased the usual relationship between peak developed wall stress, and end-diastolic pressure showed less of a descending limb than that found in the nonembolized, isolated heart.It is felt that the data summarized above have bearing on ventricular performance and coronary flow in clinical situations where hearts are perfused through pump oxygenator systems and are thereby subject to emThis work was performed during Dr. Monroe's Tenureship of a Career Development Award from the National Institutes of Health. Dr. Manasek was supported by the Medical Foundation, Inc., Boston, Mass.Received for publication 3 December 1970 and in revised form 9 March 1971. bolization from aggregated clumps fibrin.of platelets and INTRODUCTION While observing the performance of an isolated, supported canine heart in this laboratory, it was noted that if the coronary bed were embolized with small quantities of talc granules suspended in saline there was a sustained increase in coronary flow. This increase was observed while coronary perfusion pressure was maintained constant, and while heart rate and peak systolic ventricular pressure, two major determinants of coronary flow (1, 2), were also maintained constant. As one might expect such embolization to block coronary flow, this finding was not expected, and an attempt was
