The anatomic model consists of the spatial placement of the cells of different categories. Cells are placed as paralelipipedic blocks of cells, called cell blocks or simply blocks.
The blocks are defined in some order inside the model. The order is important. When two blocks overlap the cells in the last specified block replace the cells in the blocks with which it overlaps.
Inside a block, all the available space is considered filled with cells. Every cell is considered linked (in the sense that it can pass its depolarization state to) every other cell with which it has an adjacent face.
When two blocks are specified to be immediately adjacent, then links are ``forged'' between the cells of different blocks that come into close contact. The same is true between blocks that replace parts of other blocks because of overlapping and the remains of the overlapped blocks.
OBSERVATION. In theory, it is possible to build a cardiac representation which replicates the actual heart of a patient exactly, by the use of many small blocks. Nevertheless, the actual shape of the heart is usually unknown and changing, and the level of resolution of our models is not detailed enough to make such an exact description worthwhile. Instead, one should take care to preserve the general topology of the heart (for example, the fact that the posterior arterial wall is connected near its middle with the anterior one) and to approximate as close as possible the distances between the various structures (for example between the SA node and the AV node). The general shape of the electrocardigrafic waves, their succession and variability will be reproduced by such approximate anatomy--but not their exact shape and amplitude.