 In a recently published work the investigators have investigated the effect of temporary balloon occlusion of the distal IMA on coronary collateral function. 180 pairs of measurements were performed in 120 patients electively referred for coronary angiography. Levels of collateral function and myocardial ischemia were determined during two coronary balloon occlusions, the first with, the second without distal IMA balloon occlusion. Coronary collateral function, determined by collateral flow index CFI was consistently increased by ipsilateral, but not contralateral IMA balloon occlusion in the left anterior descending LAD coronary artery and the right coronary artery RCA. Furthermore, these findings were corroborated by the observed reduction in ischemia as assessed by the sensitive tool of intracoronary ECG. However, there were equivocal findings for the left circumflex coronary artery: CFI was increased by ipsilateral IMA occlusion, but the level of myocardial ischemia was unchanged. 