Although the internal mammary artery (IMA) is superior to the saphenous vein graft for bypassing certain coronary arterial obstructive lesions, such operations may predispose the patient to sternal infection or dehiscence--presumably as a result of sternal ischemia. This study was designed to measure sternal blood flow before and after median sternotomy and IMA mobilization in order to quantify the hemodynamic effects of these procedures. Rhesus primates were randomized into control, unilateral IMA-harvested, and bilateral IMA-harvested groups. After selective angiography enabled confirmation of IMA patency, 15 micron microscopheres, labeled with specific-spectra radioactive isotopes, were injected at baseline, after sternotomy, and after IMA harvesting. The sternal halves were subjected to gamma counting, and sternal circulation was accurately quantified. Our results showed that blood flow to the sternal halves in which the IMA was harvested decreased precipitously (from 4.5 to 0.8 ml/gm/min; p less than or equal to 0.001), although it remained unchanged in response to median sternotomy. This represented a 90% decrease in the mean rate of flow within the IMA-harvested sterna versus a stable flow rate for the unharvested sides. We conclude that mobilization of the internal mammary artery, as in coronary bypass procedures, significantly devascularizes the sternal half from which it was harvested.