In addition to its well established diagnostic utility, stress myocardial perfusion SPECT imaging provides an important role in risk assessment and management of patients with known or suspected coronary artery disease. Predictors of stress induced ischaemia indicating the severity or extent of CAD include transient ischaemic dilation (TID). TID is the transient dilation that occurs on a stress scan but has resolved on the resting scan. TID is routinely assessed by visual analysis of stress myocardial perfusion images relative to the resting images or manual definition of the borders to produce dilation indexes. Hence, measurement of TID is highly subjective and to date there is no gold standard for acquiring TID ratios, hi addition, error in slice selection will result in under- or over-estimation of these indexes. Moreover, the interaction of TID with other measures of disease has not been well researched. The main aims of this thesis were to evaluate TID in terms of optimal measurement, global and regional analysis, its scintigraphic correlates and the mechanisms leading to TID. Digital phantoms and monte carlo techniques were employed to determine the optimal algorithm for delineating the left ventricle and calculating transient dilation ratios. Rigid body registration was used to align stress-rest image pairs to ensure equivalent slice selection. Short axis cavity dilation was found to be the best single measure for identifying CAD but had low sensitivity. The application of combined measures of cavity dilation and cavity length proved to be a very sensitive (76%) and highly specific (96%) predictor of CAD. Transient dilation is a function of ischaemic severity and wall motion. It is not related to the rest-stress change in motion, infarcted myocardium, or wall thickening. Physical ventricular enlargement and systolic dysfunction were found to be the most likely sources of transient dilation in our patient population.