Mouse Wheel cycling. How to avoid?

[330xi]

I want to run soem code by rolling a mouse wheel.

MFC, doc/view

In Mainframe header:

afx_msg BOOL OnMouseWheel (UINT nFlags, short zDelta, CPoint pt);

In Mainframe source message map:

ON_WM_MOUSEWHEEL()

Event handler:

BOOL CMainFrame::OnMouseWheel (UINT nFlags, short zDelta, CPoint pt)
{   

    if (zDelta>0)
    {
        OnDemokey();
    }
    else
    {
        OnMinuskey();
    };  
    return TRUE;
};

If i roll forward my code cyling in "OnDemokey();" if i roll back - in "OnMinuskey();"

What have I do to make act of rolling the wheel to work like an ordinary key pressing?