Although computational studies are increasingly used to gain insight into diseases such as myocardial ischaemia,there is still considerable uncertainty about the values for many of the parameters in these studies. This isparticularly true for the bidomain conductivity values that are used in normal tissue and, even more so, inischaemic tissue, when modelling ischaemia. In this work, we extended a previous study that used a half-el-lipsoidal model and a realistic model to study subendocardial ischaemia during the ST segment, so that we couldsimulate both early and late stage ischaemia. We found that, for both stages of ischaemia, there was still the sameconnection between the degree of ischaemia and the development of features such as minima and maxima in theepicardial potential distribution (EPD), although the magnitudes of the potentials were very often less, whichmay be significant in terms of detecting them experimentally.Using uncertainty quantification associated with the ischaemic region conductivities, we also determined thatthe EPD features were sensitive to the ischaemic region extracellular normal and longitudinal conductivitiesduring early stage ischaemia, whereas, during late stage ischaemia, the intracellular longitudinal conductivitywas the most significant. However, since we again found that these effects were minor compared with the effectsoffibre rotation angle and ischaemic depth, this might suggest that it is not necessary to use different con-ductivity values inside and outside the ischaemic region when modelling ST segment subendocardial ischaemia,unless the magnitudes of the potentials are an important part of the study.