There is considerable variation among the specimens in exactly where and how the vessels were cut. Although two separate specimens are illustrated on this page to show some of the variation, you should examine several hearts in lab to familiarize yourself with the degree of variation possible. Furthermore, many of the vessels (especially the veins) can be hard to see on photographs since they are collapsed. The best way to identify the various chambers and vessels is to use a probe to trace where they go. You are strongly urged to spend as much time as possible reviewing the actual heart specimens in lab.