MergeCells Property
True if the range or style contains merged cells. Read/write Variant.
Remarks
When you select a range that contains merged cells, the resulting selection may be different from the intended selection. Use the Address property to check the address of the selected range.
Example
This example sets the value of the merged range that contains cell A3.
Set ma = Range("a3").MergeArea
If Range("a3").MergeCells Then
ma.Cells(1, 1).Value = "42"
End If