OPINION OF LINDQUIST & VENNUM P.L.L.P

                                                                     EXHIBIT 5.1


                                  [LETTERHEAD]

                                  _______, 1999


Cardia, Inc.
13754 Frontier Court
Burnsville, MN 55337

         RE:  REGISTRATION STATEMENT ON FORM S-4

Ladies and Gentlemen:

         In connection with the Registration Statement on Form S-4 filed by
Cardia, Inc., (the "Company") with the Securities and Exchange Commission on
___________, 1999 relating to the registration of 200,000 shares of Common
Stock, $.01 par value (the "Shares"), to be issued by the Company in connection
with the proposed merger of Video Learning Systems, Inc., a Minnesota
corporation, with and into the Company, please be advised that as counsel to the
Company, upon examination of such corporate documents and records as we have
deemed necessary or advisable for the purposes of this opinion, it is our
opinion that:

         1.       The Company has been duly incorporated is validly existing and
                  in good standing under the laws of the State of Minnesota.

         2.       All necessary corporate action on the part of the Company has
                  been taken to authorize the issuance of the Shares to be
                  issued in connection with such merger and, when issued
                  pursuant to the merger and paid for as contemplated by the
                  Registration Statement, the Shares will be legally issued,
                  fully paid and nonassessable.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to our firm under the heading "Legal
Matters" in the prospectus/proxy statement comprising a part of the Registration
Statement.

                                       Very truly yours,

                                       /s/ LINDQUIST & VENNUM P.L.L.P.