A simple technique to induce a reproducible functional stenosis of a coronary artery in acute experiments is described. The artery is narrowed by stepwise twisting of a thin copper wire until a zero flow occlusion of 10 sec is no longer followed by a period of diastolic reactive hyperemia. The degree of coronary stenosis is expressed as the diastolic hemodynamic resistance over the copper wire. This technique allows comparison from animal to animal and carries the possibility to follow changes in myocardial metabolism at a given degree of coronary stenosis.