diff --git a/Doc/library/heapq.rst b/Doc/library/heapq.rst
index 462b65bc7afba4..52d96600c087c0 100644
--- a/Doc/library/heapq.rst
+++ b/Doc/library/heapq.rst
@@ -306,12 +306,12 @@ entry as removed and add a new entry with the revised priority::
 Theory
 ------
 
-Heaps are arrays for which ``a[k] <= a[2*k+1]`` and ``a[k] <= a[2*k+2]`` for all
+Min-heaps are arrays for which ``a[k] <= a[2*k+1]`` and ``a[k] <= a[2*k+2]`` for all
 *k*, counting elements from 0.  For the sake of comparison, non-existing
-elements are considered to be infinite.  The interesting property of a heap is
-that ``a[0]`` is always its smallest element.
+elements are considered to be infinite.  The interesting property of a min-heap is
+that ``a[0]`` is always its smallest element. Max-heaps satisfy the reverse invariant.
 
-The strange invariant above is meant to be an efficient memory representation
+The strange min-heap invariant is meant to be an efficient memory representation
 for a tournament.  The numbers below are *k*, not ``a[k]``:
 
 .. figure:: heapq-binary-tree.svg