Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
NELSON GLEN D
   2. Issuer Name and Ticker or Trading Symbol
Cardiovascular Systems Inc [CSII] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director _____ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
651 CAMPUS DRIVE		 3. Date of Earliest Transaction (Month/Day/Year)
05/07/2010
(Street)

ST. PAUL, MN 55112		 4. If Amendment, Date Original Filed(Month/Day/Year)
 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)		 4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		 5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)		 6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)		 7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 05/07/2010   P   33,000 A $ 4.7895 (2) 174,702 D  
Common Stock 05/10/2010   P   30,000 A $ 4.864 (3) 204,702 D  
Common Stock 05/11/2010   P   10,000 A $ 4.9824 (4) 214,702 D  
Common Stock               246,524 I Held by LLC (1)

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)		 5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)		 6. Date Exercisable and Expiration Date
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(Instr. 3 and 4)		 8. Price of Derivative Security
(Instr. 5)		 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)		 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)		 11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (right to buy) $ 12.37             12/01/2005 11/30/2015 Common Stock 9,705   9,705 D  
Stock Option (right to buy) $ 9.28             04/21/2010 11/30/2014 Common Stock 6,470   6,470 D  
Stock Option (right to buy) $ 8.83             12/19/2006 12/18/2016 Common Stock 12,940   12,940 D  
Stock Option (right to buy) $ 7.9             10/09/2007 10/08/2017 Common Stock 4,322   4,322 D  
Stock Option (right to buy) $ 11.38             11/13/2007 11/12/2017 Common Stock 15,087   15,087 D  
Warrant $ 8.78             07/19/2006 07/19/2011 Common Stock 12,131   12,131 I Held by LLC (1)
Warrant $ 9.28             09/12/2008 09/12/2013 Common Stock 53,916   53,916 I Held by LLC (1)
Warrant $ 8.83             02/25/2009 02/24/2014 Common Stock 56,558   56,558 I Held by LLC (1)
Restricted Stock Units (5)               (5)   (5) Common Stock 5,714   5,714 D  
Restricted Stock Units (6)               (6)   (6) Common Stock 11,628   11,628 D  

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
NELSON GLEN D
651 CAMPUS DRIVE
ST. PAUL, MN 55112		   X      

Signatures

 /s/ John R. Remakel as Attorney-in-Fact for Glen D. Nelson pursuant to Power of Attorney previously filed.   05/11/2010
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) Shares are held by GDN Holdings, LLC, of which Dr. Nelson is the sole owner.
(2) The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $4.53 to $5.00 inclusive. The reporting person undertakes to provide Cardiovascular Systems, Inc., any security holder of Cardiovascular Systems, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.
(3) The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $4.77 to $4.95 inclusive. The reporting person undertakes to provide Cardiovascular Systems, Inc., any security holder of Cardiovascular Systems, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.
(4) The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $4.87 to $5.00 inclusive. The reporting person undertakes to provide Cardiovascular Systems, Inc., any security holder of Cardiovascular Systems, Inc. or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote.
(5) Each restricted stock unit represents the right to receive a payment from CSI equal in value to the market price per share of CSI common stock on the date of payment and shall be payable in shares of the Company's Common Stock beginning six months following the termination of each director's board membership.
(6) Each restricted stock unit represents the right to receive a payment from CSI equal in value to the market price per share of CSI common stock on the date of payment, and shall be payable in shares of the Company's Common Stock beginning six months following the termination of each director's board membership; provided, however, that the restricted stock units vest in equal quarterly amounts of 2,907 on each of 9/30/2009, 12/31/2009, 3/31/2010 and 6/30/2010.

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