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                                                                    EXHIBIT 4.10

NEITHER THIS SUBORDINATED CONVERTIBLE DEBENTURE NOR THE COMMON STOCK INTO WHICH
IT IS CONVERTIBLE HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 OR THE
SECURITIES LAWS OF ANY STATE AND NEITHER MAY BE SOLD NOR OTHERWISE TRANSFERRED,
EXCEPT AS OTHERWISE PROVIDED HEREIN, IN THE ABSENCE OF AN EFFECTIVE
REGISTRATION STATEMENT UNDER SUCH ACT OR AN OPINION OF COUNSEL REASONABLY
ACCEPTABLE TO THE ISSUER HEREOF THAT SUCH REGISTRATION IS NOT REQUIRED.

                     4% SUBORDINATED CONVERTIBLE DEBENTURE

                               DUE APRIL 1, 2005

$___________                      April 1, 2002            Nashville, Tennessee

         SYMBION, INC., a Tennessee corporation ("Symbion"), for value
received, hereby promises to pay to ____________________ (the "Holder") the
principal amount of _______________ ________________________ Dollars
($_________) (or so much thereof as shall not have been previously paid) plus
accrued and unpaid interest on April 1, 2005, or such earlier date provided
below. The unpaid principal of this Debenture remaining outstanding from time
to time shall bear interest at the rate of four percent (4%) per annum
(computed on the basis of a 365-day year) from the date hereof until payment of
all outstanding principal and interest hereunder or conversion of this
Debenture. Interest accrued hereunder shall be payable in arrears on April 1 of
each year, commencing April 1, 2003. Payments of principal and interest on this
Debenture shall be made to the Holder in lawful money of the United States of
America at the address of the Holder set forth in Section 6 hereof, or at such
other office or agency as the Holder shall have designated by written notice to
Symbion.

         Subject to the conversion right of the Holder set forth in Section 2,
Symbion shall have the right to prepay this Debenture in whole or in part,
without the prior written consent of the holder hereof, upon thirty (30) days
prior written notice to the Holder.

         This Debenture may not be transferred by the Holder, in whole or in
part.

1.       EVENTS OF DEFAULT. If any of the following conditions or events (each
an "Event of Default" and collectively, the "Events of Default") shall occur
and be continuing:

         (a)      if Symbion shall default in the payment of any principal on
                  this Debenture when same becomes due and payable and such
                  payment shall not have been made within thirty (30) days
                  after written notice of default shall have been received by
                  Symbion from the holder of this Debenture, except a default
                  in the payment of principal within thirty (30) days after
                  maturity, in which event no notice of default is required; or

         (b)      if Symbion shall default in the payment of any interest on
                  the Debenture when the same becomes due and payable and such
                  default shall continue more than thirty (30) days after
                  written notice of default shall have been received by Symbion
                  from the holder of this Debenture; or


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         (c)      if Symbion shall make an assignment for the benefit of
                  creditors, or shall admit in writing its inability to pay its
                  debts as they become due, or shall file a voluntary petition
                  in bankruptcy, or shall be adjudicated a bankrupt or
                  insolvent, or shall file any petition or answer seeking for
                  itself any reorganization, arrangement, composition,
                  readjustment, liquidation, dissolution or similar relief
                  under any current or future statute, law or regulation
                  relating to bankruptcy or insolvency, or shall file any
                  answer admitting or not contesting the material allegations
                  of a petition filed against Symbion in any such proceeding,
                  or shall seek or consent to or acquiesce in the appointment
                  of any custodian, trustee, receiver or liquidator of Symbion
                  or of all or any substantial part of the properties of
                  Symbion, or if Symbion or its Board of Directors shall take
                  any action looking to the dissolution or liquidation of
                  Symbion; or

         (d)      if, within sixty (60) days after the commencement of an
                  action against Symbion seeking any reorganization,
                  arrangement, composition, readjustment, liquidation,
                  dissolution or similar relief under any present or future
                  statute, law or regulation, such action shall not have been
                  dismissed or all orders or proceedings thereunder affecting
                  the operations or the business of Symbion stayed, or if the
                  stay of any such order or proceeding shall thereafter be set
                  aside, or if, within sixty (60) days after the appointment
                  without the consent or acquiescence of Symbion or any
                  custodian, trustee, receiver or liquidator of Symbion or of
                  all of any substantial part of the properties of Symbion,
                  such appointments, shall not have been vacated;

then, and in any such event, the holder hereof may at any time (unless all
defaults shall theretofore have been remedied) at its option, by written notice
to Symbion, declare this Debenture to be due and payable, whereupon this
Debenture shall forthwith mature and become due and payable, together with
interest accrued and unpaid hereon, without presentment, demand, protest or
notice, all of which are hereby waived.

2.       CONVERSION.

         2.1.     Conversion Right. Beginning on the date hereof and continuing
thereafter until this Debenture shall be paid in full or prepaid in full, as
the case may be, this Debenture may, at the election of the holder hereof upon
thirty (30) days prior written notice by the Holder hereof or ten (10) days
prior written notice given after a notice of prepayment given by Symbion as
described in the preamble hereto to Symbion of such election, be converted into
shares (the "Conversion Shares") of common stock, no par value, of Symbion (the
"Common Stock") at a price per share of $3.13 (the "Conversion Price"), subject
to adjustment as provided in Section 2.5 hereof.

         2.2      Manner of Conversion. This Debenture may be converted by the
holder hereof by presentment of this Debenture, accompanied by written election
stating that such holder elects to convert all of the principal amount thereof
and stating the name or names, together with addresses, in which the Conversion
Shares are to be issued. All of the principal amount must be tendered.
Conversion shall be deemed to have been affected immediately prior to the close
of business on the date on which this Debenture shall have been so surrendered
to Symbion; and at such time the rights of the holder as to the Debenture so
converted shall cease, and the person in whose name or names any certificate or
certificates for Conversion


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Shares (or other securities) shall be issuable upon such conversion shall be
deemed to have become the holder or holders of record thereof.

         2.3      Automatic Conversion. This Debenture shall automatically be
converted, with no further action required to be taken by Symbion or the holder
hereof, upon the closing of an initial public offering (the "Initial Public
Offering") pursuant to an effective registration statement under the Securities
Act of 1933, as amended, covering the offer and sale of the capital stock of
Symbion, into the number of fully paid and non-assessable shares of Common
Stock equal to the quotient of (x) the unpaid principal amount of this
Debenture outstanding on the closing date of the Initial Public Offering
divided by (y) the Conversion Price then in effect (after giving effect to any
adjustments pursuant to Section 2.5 below). Immediately upon conversion as
provided herein, the holder shall be deemed to be the holder of record of the
Common Stock issuable upon conversion of this Debenture, notwithstanding that
the share register of Symbion shall then be closed or that certificates
representing the Common Stock shall not then actually be delivered to such
person. Upon written notice from Symbion, the holder of this Debenture so
converted shall promptly surrender this Debenture to Symbion at its principal
place of business to be maintained by it (or at such other office or agency of
Symbion as Symbion may designate by such notice to the holder).

         2.4.     Accrued Interest. Symbion will pay to the holder upon
conversion of this Debenture any accrued but unpaid interest in cash on the
principal amount so converted up to and including the date of conversion.

         2.5.     Adjustment of Conversion Price. The Conversion Price shall be
adjusted from time to time as follows:

                  2.5.1.   In case Symbion shall hereafter (i) pay a stock
dividend or make a stock distribution of shares of Common Stock with respect to
the Common Stock, (ii) subdivide its outstanding Common Stock into a greater
percentage of Common Stock, (iii) combine its outstanding Common Stock into a
smaller amount of Common Stock, or (iv) issue by reclassification of its Common
Stock any other security of Symbion, the Conversion Price in effect immediately
prior to such action shall be adjusted so that the holder of this Debenture or
any portion hereof thereafter surrendered for conversion shall be entitled to
receive the amount of Common Stock or other capital stock of Symbion which he
would have owned immediately following such action had this Debenture or any
remaining portion hereof been converted immediately prior thereto. All
adjustments made pursuant to this subsection 2.5.1 shall become effective
immediately after the record date in the case of a dividend or distribution and
shall become effective immediately after the effective date in the case of a
subdivision, combination or reclassification. If, as a result of an adjustment
made pursuant to this subsection 2.5.1, the holder of this Debenture or any
remaining portion hereof thereafter surrendered for conversion shall become
entitled to receive the Conversion Shares and other securities of Symbion, the
Board of Directors of Symbion shall reasonably and in good faith determine the
allocation of the adjusted Conversion Price between or among the Conversion
Shares and such other securities.

                  2.5.2.   If the amount of any single adjustment of the
Conversion Price required pursuant to subsection 2.5.1 would be less than one
cent ($.01) at the time such adjustment is otherwise so required to be made,
such amount shall be carried forward and adjustment with respect thereto made
at the time of and together with any subsequent adjustment


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which, together with such amount and any other amount or amounts so carried
forward, shall aggregate at least one cent ($.01) when the Conversion Price is
adjusted.

         2.6.     Reservation of Common Stock Issuable on Conversion. Symbion
will at all times reserve and keep available, solely for issuance and delivery
upon the conversion of this Debenture, the amount of Common Stock, whether
authorized but unissued shares reserved by it which are free from preemptive
rights or issued shares which have been reacquired by it, from time to time
issuable upon the conversion of this Debenture at the time outstanding. Symbion
hereby covenants that all such securities shall be duly authorized and, when
issued upon such conversion, shall be validly issued and, in the case of
shares, fully paid and nonassessable with no liability on the part of the
holders thereof.

3.       SUBORDINATION.

         3.1.     Definition. For purposes of this Section 3.1 the term "Senior
Debt" shall mean any indebtedness for borrowed money, the payment of which
Symbion is at the time of determination responsible or liable as obligor,
guarantor or otherwise, other than (a) indebtedness as to which, in the
instrument creating or evidencing the same or pursuant to which the same is
outstanding, it is expressly provided that such indebtedness is junior and
subordinate to other indebtedness and obligations of Symbion, (b) indebtedness
which by its terms refers explicitly to this Debenture and states that such
indebtedness shall not be senior thereto and shall be equally subordinated and
equally junior, and (c) indebtedness of Symbion in respect of this Debenture.
Senior Debt shall continue to be Senior Debt and entitled to the benefits of
the subordination provisions set forth herein irrespective of any amendment,
modification, of waiver of any term of the Senior Debt or extension or renewal
of the Senior Debt.

         3.2.     Debenture Subordinate to Senior Debt. Symbion, for itself,
its successors and assigns, covenants and agrees, and each holder, by its
acceptance of this Debenture or any portion hereof, likewise covenants and
agrees, that this Debenture shall be subordinated and subject, to the extent
and in the manner herein set forth, in right of payment to the prior payment in
full of all Senior Debt. The provisions of this Section 3 are made for the
benefit of all holders of Senior Debt, and any such holder may proceed to
enforce such provisions.

         3.3.     Payment Over of Proceeds Upon Dissolution, Etc. No payment on
account of principal of (or premium, if any) or interest on this Debenture
shall be made, if any default or event of default with respect to any Senior
Debt, which permits or with the giving of notice or passage of time or both
would permit the holders thereof (or a trustee on their behalf) to accelerate
the maturity thereof, shall have occurred and be continuing and Symbion shall
have received written notice thereof from the holders of at least ten percent
(10%) in principal amount of any kind or category of any Senior Debt (or the
representative or representatives of such holders).

         In the event this Debenture is declared due and payable before the
maturity date hereof, or upon any payment or distribution of assets of Symbion
of any kind or character, whether in cash, property or securities, to creditors
upon any dissolution or winding-up or total or partial liquidation or
reorganization of Symbion, whether voluntary or paid in full or in bankruptcy,
insolvency, receivership or other proceedings, or upon any assignment by
Symbion for the benefit of creditors or any other marshalling of the assets of
Symbion, all principal of (and premium, if any) and interest due or to become
due upon all Senior Debt


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(including any interest thereon occurring after the commencement of any such
proceeding) shall first be paid in full before the holder of this Debenture
shall be entitled to retain any assets so paid or distributed in respect of
this Debenture (for principal, premium, if any, or interest); and upon such
dissolution or winding-up or liquidation or reorganization or assignment or
marshalling of assets, any rights or distribution of assets, any payment or
distribution of assets of Symbion of any kind or character; whether in cash,
property or securities, to which the holders of this Debenture would be
entitled, except for the provisions of this Section, shall be paid by Symbion
or by any receiver, trustee in bankruptcy, liquidating trustee, agent or other
person making such payment or distribution, or by the holders of this Debenture
if received by them or it, directly to the holders of Senior Debt (pro rata to
each such holder as their interests may appear on the holders of the respective
amounts of Senior Debt held by such holder, including any interest thereon
accruing after the commencement of any such proceedings) or their
representatives, to the extent necessary to pay all Senior Debt in full, after
giving effect to any concurrent payment or distribution to or for the holders
of Senior Debt, before any payment or distribution is made to the holders of
this Debenture.

         No holder of Senior Debt shall be prejudiced in his right to enforce
subordination of this Debenture by any act or failure to act on the part of
Symbion.

         Subject to the payment in full of all Senior Debt, the holder of this
Debenture shall be subrogated (equally and ratably with the holders of all
indebtedness of Symbion which, by its express terms, ranks on a parity with
this Debenture and is entitled to like rights of subrogation) to the rights of
the holders of Senior Debt to receive payments or distributions of assets of
Symbion applicable to the Senior Debt until this Debenture shall be paid in
full. For purposes of such subrogation, no payments or distributions on the
Senior Debt pursuant to this Section shall, as between Symbion, its creditors
other than the holders of Senior Debt, and the holder of this Debenture, be
deemed to be a payment by Symbion to or on account of the Senior Debt, and no
payments or distributions to the holders of this Debenture of assets by virtue
of the subrogation herein provided for shall, as between Symbion, its creditors
other than the holder of Senior Debt, and the holders of this Debenture, be
deemed to be a payment to or on account of this Debenture. The provisions of
this Section are and are intended solely for the purpose of defining the
relative rights of the holder of this Debenture, on the one hand, and the
holders of Senior Debt, on the other hand, and nothing contained in this
Section or in this Debenture is intended to or shall impair the obligation of
Symbion, which is unconditional and absolute, to pay the principal of (and
premium, if any) and interest on this Debenture as and when the same shall
become due and payable in accordance with its terms, or to affect the relative
rights of the holders of this Debenture and creditors of Symbion other than the
holders of Senior Debt, nor shall anything herein prevent the holders of this
Debenture from exercising all remedies otherwise permitted by applicable law
upon default under this Debenture, subject to the rights, if any, under this
Section, of the holders of Senior Debt in respect of cash, property or
securities of Symbion otherwise payable or delivered to the holders of this
Debenture upon the exercise of any such remedy.

         Nothing contained in this Section 3.3 shall prevent conversion of this
Debenture.

4.       GOVERNING LAW. This Debenture shall be governed by the laws of the
State of Delaware.


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5.       INTEREST RATE. Notwithstanding any other provision of this Debenture
or in any documents relating hereto, the holder of this Debenture shall not be
entitled to receive, collect, reserve or apply as interest, any amount in
excess of the maximum rate of interest permitted to be charged by applicable
law or regulations, as amended or enacted from time to time. In the event a
holder hereof ever receives, collects, reserves or applies as interest any such
excess, such amount which would be excessive interest shall be deemed a partial
prepayment of principal and treated hereunder as such or, if the principal
indebtedness evidenced hereby is paid in full, any remaining excess funds shall
immediately be paid to Symbion. In determining whether or not the interest paid
or payable, under any specific contingency, exceeds the maximum lawful rate of
interest, Symbion and the holder of this Debenture, to the maximum extent
permitted under applicable law, shall exclude voluntary prepayments and the
effects thereof; provided, that if the indebtedness is paid and performed in
full prior to maturity hereof, and if the interest received for the actual
period of existence hereof exceeds the maximum lawful rate of interest, the
holder hereof shall refund to Symbion the amount of such excess or credit the
amount of such excess against the principal portion of the indebtedness, as of
the date it was received and, in such event, the holder hereof shall not be
subject to any penalties payable to Symbion provided by any laws for
contracting for, charging, reserving or receiving interest in excess of the
maximum lawful rate of interest.

6.       NOTICES. All notices and communications required or permitted
hereunder shall be in writing and shall be sufficiently given and deemed to
have been received: (i) upon personal delivery or delivery by overnight
courier, (ii) when sent by facsimile or telecopier, with written confirmation
of receipt, or (iii) if mailed, upon the first to occur of actual receipt or
seventy-two (72) hours after being placed in the United States mail, postage
prepaid, registered or certified snail, receipt requested, in each case
addressed as follows:

         To the Holder at such address as the Holder has designated in writing
to Symbion.

         To Symbion:         Symbion, Inc.
                             3401 West End Avenue, Suite 760
                             Nashville, Tennessee 37203
                             Facsimile No.: (615) 386-6690
                             Attention: President

or such other address as a party may designate by notice to the other parties
hereto.


                    [The next page is the signature page.]


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Executed April 1, 2002:


                                    SYMBION INC.


                                    By:
                                       ----------------------------------------
                                       Kenneth C. Mitchell
                                       Vice President


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