CONTACT CARDS DISAPPEARED FROM MACBOOK PRO

Contact Cards have disappeared suddenly from my MacBook Pro. They show up on Contacts on iCloud and on my iPad but not my Mac. The names of contacts are still listed in the middle column of the contacts' window but the right column of that window is blank with "No Cards" only on it. Why has this happened? Yesterday I followed on my iPad instructions to eliminate double holidays entries on the calendar, but did not do anything with Contacts? What do I need to do to restore the Contact Cards on my MacBook Pro?