An implantable medical device comprising a coronary perfusion measurement unit is adapted to measure and determine parameters related to coronary perfusion of heart tissue. The parameters include time periods and perfusion magnitudes. The coronary perfusion measurement unit is configured to determine a time period T related to a perfusion event of a coronary vessel and including includes a reperfusion time period, where a perfusion event is defined as a decrease of coronary perfusion followed by reperfusion, and to generate a time period signal in dependence thereto. The implantable medical device further comprises a coronary flow calculation unit that is adapted to receive the time period signal and that is adapted to process the time period and to generate an ischemia risk indicating index I in dependence of the time period.
