Background. In the selection of patients eligible for minimally invasive coronary artery bypass grafting (MICABG), knowledge about the pathophysiologic significance of individual coronary stenoses is important. Only if the lesion amenable to MICABG can be identified as the culprit lesion, and other lesions can be demonstrated not to be responsible for reversible ischemia, will MICABG be an appropriate procedure. Methods. By simultaneous measurement of mean aortic pressure and transstenotic coronary pressure, a pathophysiologic index can be obtained that specifically indicates the influence of an epicardial coronary stenosis on maximum achievable blood flow of the supplied myocardial territory. This index is called myocardial fractional flow reserve (FFR(myo)). Results. Myocardial fractional flow reserve is a reliable, lesion-specific index for determining whether a particular stenosis is responsible for reversible myocardial ischemia. If FFR(myo) is less than 0.75, revascularization is indicated, whereas if FFR(myo) is greater than 0.75, revascularization usually is not warranted. Moreover, in contrast to classic coronary flow or flow velocity reserve, FFR(myo) is independent of changes in heart rate, blood pressure, and contractility, and also accounts for the contribution of collaterals. Conclusions. Pressure-derived FFR(myo) is an accurate pathophysiologic index for reliable identification of functionally significant epicardial lesions and can be obtained easily and quickly during routine cardiac catheterization. Therefore, FFR(myo) facilitates clinical decision-making with respect to the appropriateness of MICABG.