Myocardial perfusion imaging during adenosine induced coronary hyperaemia is a highly sensitive method for diagnosing coronary artery disease. Most perfusion defects reflect heterogeneity in coronary blood flow in the territories of normal and diseased coronary arteries. Myocardial ischaemia can occur, however, due to subendocardial hypoperfusion and coronary artery steal. Evidence for myocardial ischaemia is more difficult to document in clinical than in experimental studies, and includes abnormalities in the ST segment, wall motion, haemodynamic variables, metabolism, and coronary blood flow responses. Using these indices, myocardial ischaemia may occur in some patients with coronary artery disease but it is not a prerequisite for the development of perfusion abnormalities and for the diagnosis of coronary artery during adenosine stress testing.