A federal judge has conditionally certified a nationwide class action for medical monitoring on behalf of consumers who took the fen-phen diet drug combination for at least 30 days and now fear an increased risk of heart valve disease.

In a 41-page opinion handed down late yesterday, Senior U.S. District Judge Louis C. Bechtle rejected the argument that such a massive class action would be impossible to manage due to factors that make each individual plaintiff’s claim unique or the need to apply the laws of all 50 states.