The mass differencemL—mS constrains heavy-quark masses. The bounds are extended into the region abovemW/α½. We find a lowermU bound of 7 TeV for the scenariomC≫mU. Effects that could change this result are examined. Values ofmU smaller thanmW/α½ seem to be excluded. The applied methods and obtained results should help to shed more light on the issue of indirectCP violation.