Now envision a region of diseased or depressed myocardium, (the brown region in the figure-B), having a slower conduction velocity and a longer refractory period than the otherwise normal myocardium (the white region-A). Such regions my actually exist, caused by one of several pathological conditions such as a prior myocardial infarction. The figure illustrates a non-premature beat that conducts normally through the normal region, but slowly through the diseased region. It will distinguish itself at point X because the tissue on both sides of the point, having just been excited, will be refractory.