A system of loose leaf diagrams is presented for the purpose of portraying the various types of cardiac structure. Appropriate assembly of the diagrams may be used to define the anatomic details in a given case of which a permanent machine-copy may be made and the basic diagrams re-used. The diagrams may be used as teaching devices to illustrate the interrelationships between (1) transposition of the great vessels, (2) inversion of the various cardiac chambers and great vessels, and (3) dextrocardia. The material lends itself to illustration of the concept of “four normal hearts;” that is, the fact that although structurally different, there are four anatomic patterns of heart which allow a normal route for the flow of blood. The diagrams also may be used to illustrate certain features about potential cardiac transplantation. These include the point that for the recipient with a certain body type (situs solitus or situs inversus), normal channels for the flow of blood may be obtained from a donor with one of three types of cardiac structure. These are either the normal or that of corrected transposition of the same body type as the recipient or complete transposition in a donor with the opposite body type from that of the recipient.