Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim trg As Range, etat As Boolean, i As Long
Set trg = Target(1, 1)
If trg.Column = 1 And trg.Row > 2 Then
If trg.MergeCells Then
Application.ScreenUpdating = False
etat = Cells(trg.Row + 1, 1).EntireRow.Hidden
For i = trg.Row + 1 To Rows.Count
If Not IsDate(Cells(i, "a").Value) Then trg.Offset(, 1).Activate: Exit Sub
Cells(i, "a").EntireRow.Hidden = Not etat
Next i
End If
End If
End Sub