The internal nodes point to leaf nodes. The leaf nodes contain pointers to the heap (table). At least with a B+Tree, the internal nodes only point to the leaf n

The internal nodes point to leaf nodes. The leaf nodes contain pointers to the heap (table). At least with a B+Tree, the internal nodes only point to the leaf nodes in the same B+Tree structure, and not to "data proper". So the leaf nodes, which are often about 99% of the total, contain index tuples that point to the "data proper". The internal nodes have index tuples too, but those are only used to get to the leaf nodes.