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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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) 04/21/2010 (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               141,702 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

04/21/2010

D(2)

9,705

(2)

11/30/2010

Common Stock

9,705

$ 0

0

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

(4)

(4)

(4)

Common Stock

5,714

5,714

D

Restricted Stock Units

(5)

(5)

(5)

Common Stock

11,628

11,628

D

Stock Option (right to buy)

$ 9.28

04/21/2010

A

6,470

(3)

11/30/2014

Common Stock

6,470

$ 0

6,470

D

Stock Option (right to buy)

$ 12.37

04/21/2010

A(2)

9,705

(2)

11/30/2015

Common Stock

9,705

$ 0

9,705

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.		04/23/2010
**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 two reported transactions involved an amendment of an outstanding option, resulting in the deemed cancellation of the "old" option and the grant of a replacement option. The option was originally granted on December 1, 2005 and is fully exercisable.
(3)	Fully exercisable.
(4)	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.
(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; 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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