Morphological signs of severe ischaemic injury are well known. However, we still lack knowledge about how indices of milder injuries are related on a cellular level. In a previous study we have reported on the sequence of alterations across the border zone in cat hearts subjected to 3 h of coronary occlusion. In the present study, which elaborates that study, we have examined the relationship between morphological variables in serial sections of 220 myocytes within the border zone. In cells with intact sarcolemma and no chromatin changes, the fractional volume of cytoplasm has a bimodal distribution indicating cells with and without oedema. Whereas cells with focal disruptions of the sarcolemma have a moderate oedema, usually localized submembranously, cells with extensive sarcolemmal fragmentation have an extensive oedema. A mild oedema is seen before other signs of severe cell injury, even though more extensive oedema is closely associated with sarcolemmal fragmentation. The fractional volume of mitochondria was smaller, whereas the fractional volume of lipid droplets was larger in cells with oedema than in cells without oedema.