diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index bf2b9b19e7..6524fc44a5 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -360,14 +360,13 @@ heap_setscanlimits(TableScanDesc sscan, BlockNumber startBlk, BlockNumber numBlk
 }
 
 /*
- * heapbuildvis - Utility function for heap scans.
+ * heap_page_prep - Prepare the current scan page to be scanned in pagemode
  *
- * Given a page residing in a buffer saved in the scan descriptor, prune the
- * page and determine which of its tuples are all visible, saving their offsets
- * in an array in the scan descriptor.
+ * Preparation currently consists of 1. prune the scan's rs_cbuf page, and 2.
+ * fill the rs_vistuples array with the OffsetNumbers of visible tuples.
  */
 void
-heapbuildvis(TableScanDesc sscan)
+heap_page_prep(TableScanDesc sscan)
 {
 	HeapScanDesc scan = (HeapScanDesc) sscan;
 	Buffer		buffer = scan->rs_cbuf;
@@ -381,6 +380,8 @@ heapbuildvis(TableScanDesc sscan)
 
 	Assert(BufferGetBlockNumber(buffer) == block);
 
+	/* ensure we're not accidentally being used when not in pagemode */
+	Assert(scan->rs_base.rs_flags & SO_ALLOW_PAGEMODE);
 	snapshot = scan->rs_base.rs_snapshot;
 
 	/*
@@ -454,10 +455,10 @@ heapbuildvis(TableScanDesc sscan)
 }
 
 /*
- * heapfetchbuf - subroutine for heapgettup()
+ * heapfetchbuf - read and pin the given MAIN_FORKNUM block number.
  *
- * This routine reads the specified block of the relation into a buffer and
- * returns with that pinned buffer saved in the scan descriptor.
+ * Read the specified block of the scan relation into a buffer and pin that
+ * buffer before saving it in the scan descriptor.
  */
 static inline void
 heapfetchbuf(HeapScanDesc scan, BlockNumber block)
@@ -878,8 +879,11 @@ heapgettup_pagemode(HeapScanDesc scan,
 	 */
 	while (block != InvalidBlockNumber)
 	{
+		/* read the page */
 		heapfetchbuf(scan, block);
-		heapbuildvis((TableScanDesc) scan);
+
+		/* prune the page and determine visible tuple offsets */
+		heap_page_prep((TableScanDesc) scan);
 		page = BufferGetPage(scan->rs_cbuf);
 		linesleft = scan->rs_ntuples;
 		lineindex = ScanDirectionIsForward(dir) ? 0 : linesleft - 1;
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index f4f670e9b2..a4451c24b4 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -2352,6 +2352,7 @@ heapam_scan_sample_next_block(TableScanDesc scan, SampleScanState *scanstate)
 	if (hscan->rs_nblocks == 0)
 		return false;
 
+	/* release previous scan buffer, if any */
 	if (BufferIsValid(hscan->rs_cbuf))
 	{
 		ReleaseBuffer(hscan->rs_cbuf);
@@ -2403,7 +2404,7 @@ heapam_scan_sample_next_block(TableScanDesc scan, SampleScanState *scanstate)
 
 	hscan->rs_cblock = blockno;
 
-	if (!BlockNumberIsValid(hscan->rs_cblock))
+	if (!BlockNumberIsValid(blockno))
 	{
 		hscan->rs_inited = false;
 		return false;
@@ -2412,22 +2413,19 @@ heapam_scan_sample_next_block(TableScanDesc scan, SampleScanState *scanstate)
 	Assert(hscan->rs_cblock < hscan->rs_nblocks);
 
 	/*
-	 * We may scan multiple pages before finding tuples to yield or finishing
-	 * the scan. Since we want to check for interrupts at least once per page,
-	 * do so here.
+	 * Be sure to check for interrupts at least once per page.  Checks at
+	 * higher code levels won't be able to stop a sample scan that encounters
+	 * many pages' worth of consecutive dead tuples.
 	 */
 	CHECK_FOR_INTERRUPTS();
 
 	/* Read page using selected strategy */
 	hscan->rs_cbuf = ReadBufferExtended(hscan->rs_base.rs_rd, MAIN_FORKNUM,
-										hscan->rs_cblock, RBM_NORMAL, hscan->rs_strategy);
+										blockno, RBM_NORMAL, hscan->rs_strategy);
 
-	/*
-	 * If pagemode is allowed, prune the page and build an array of visible
-	 * tuple offsets.
-	 */
+	/* in pagemode, prune the page and determine visible tuple offsets */
 	if (hscan->rs_base.rs_flags & SO_ALLOW_PAGEMODE)
-		heapbuildvis(scan);
+		heap_page_prep(scan);
 
 	hscan->rs_inited = true;
 	return true;
@@ -2590,7 +2588,7 @@ SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,
 	if (scan->rs_flags & SO_ALLOW_PAGEMODE)
 	{
 		/*
-		 * In pageatatime mode, heapgetpage() already did visibility checks,
+		 * In pageatatime mode, heap_page_prep() already did visibility checks,
 		 * so just look at the info it left in rs_vistuples[].
 		 *
 		 * We use a binary search over the known-sorted array.  Note: we could
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 4d324c78e5..e8a211cf1b 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -267,7 +267,7 @@ extern TableScanDesc heap_beginscan(Relation relation, Snapshot snapshot,
 									uint32 flags);
 extern void heap_setscanlimits(TableScanDesc sscan, BlockNumber startBlk,
 							   BlockNumber numBlks);
-extern void heapbuildvis(TableScanDesc sscan);
+extern void heap_page_prep(TableScanDesc sscan);
 extern void heap_rescan(TableScanDesc sscan, ScanKey key, bool set_params,
 						bool allow_strat, bool allow_sync, bool allow_pagemode);
 extern void heap_endscan(TableScanDesc sscan);