AMENDMENT NO. 4 TO INVESTORS’ RIGHTS AGREEMENT

Exhibit 4.6

AMENDMENT NO. 4 TO INVESTORS’ RIGHTS AGREEMENT

     THIS AMENDMENT NO. 4 TO INVESTORS’ RIGHTS AGREEMENT is entered into effective this 12th day of September, 2008 (this “Amendment No. 4”), by and among Cardiovascular Systems, Inc., a Minnesota corporation (the “Company”), Silicon Valley Bank (“SVB”), and the Investors signatory hereto.

RECITALS

     WHEREAS, this Amendment No. 4 amends an Investor’s Rights Agreement, dated July 19, 2006 (the “Investors’ Rights Agreement”) by and between the Company and the “Investors” set forth on Schedule A thereto and “Stockholders” set forth on Schedule B thereto, as amended by Amendment No. 1 to Investor’s Rights Agreement, dated October 3, 2006 by and between the Company, ITX International Equity Corp. and the “Investors” signatory thereto, and Amendment No. 2 to Investor’s Rights Agreement, dated September 19, 2007 by and between the Company, the Series A-1 Convertible Preferred Stockholders and the “Investors” signatory thereto, and Amendment No. 3 to Investor’s Rights Agreement, dated December 17, 2007 by and between the Company, the Series B Convertible Preferred Stockholders and the “Investors” signatory thereto;

     WHEREAS, the Company has agreed to issue a warrant to SVB to purchase up to 13,000 shares of Series B Convertible Preferred Stock (the “Warrant”) in connection with that certain Loan and Security Agreement between SVB and the Company, dated September 12, 2008;

     WHEREAS, the Warrant provides that SVB will become a party to the Investor’s Rights Agreement upon exercise or conversion of the Warrant;

     WHEREAS, on July 22, 2008, the Company’s Board of Directors approved the SVB transaction, including the issuance of the Warrant and the granting of registration rights thereunder pursuant to the Investors’ Rights Agreement; and

     WHEREAS, Investors executing this Amendment No. 4 hold at least 66²/₃% of the combined voting power of the outstanding shares of Series A Preferred Stock and any Common Stock issued upon conversion of the Series A Preferred Stock.

     NOW THEREFORE, in consideration of the mutual covenants and agreements contained in this Amendment No. 4, the sufficiency of which is hereby acknowledged, the parties hereto agree as set forth below:

	1.		Defined Terms. Capitalized terms not defined herein shall have the meanings ascribed to them in the Investor’s Rights Agreement.
	2.		The Series B Convertible Preferred Stock to be issued pursuant to the Warrant shall be deemed additional shares of Series A Preferred Stock for purposes of the Investor’s Rights Agreement. For purposes of clarity, it is acknowledged and agreed that any shares of Common Stock that are issued upon conversion of any such Series B Convertible

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			Preferred Stock shall be deemed “Series A Registrable Securities” for purposes of the Investor’s Rights Agreement.
	3.		Automatically upon the exercise or conversion of the Warrant by SVB (or any successors or permitted transferees or assigns under the Warrant) (the “Warrant Holder”), Schedule A shall be amended to add the Warrant Holder as an Investor and the Warrant Holder shall be deemed an Investor as that term is used in the Investor’s Rights Agreement.
	4.		This Amendment No. 4 may be executed in any number of original or facsimile counterparts, and each such counterpart hereof shall be deemed to be an original instrument, but all such counterparts together shall constitute but one agreement. Any counterpart or other signature to this Amendment No. 4 that is delivered by facsimile shall be deemed for all purposes as constituting good and valid execution and delivery by such party of this Amendment No. 4.
	5.		Except as set forth herein, all other terms and conditions of the Investor’s Rights Agreement remain the same.
	6.		This Amendment No. 4 shall be effective upon the issuance of the Warrant to SVB. If the Warrant is not so issued, this Amendment No. 4 shall have no force or effect.

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     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

	CARDIOVASCULAR SYSTEMS, INC.
	By:	/s/ Xxxxxxxx X. Xxxxxxxxx
		Name:	Xxxxxxxx Xxxxxxxxx
		Title:	Chief Financial Officer

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

		EASTON XXXX CAPITAL PARTNERS, L.P.
		By:		EHC GP, L.P. its General Partner
		By:		EHC GP, Inc., its General Partner
		By:		/s/ Xxxxxxx X. Xxxxxxxxx
				Name: Xxxxxxx X. Xxxxxxxxx
				Title: Vice President and Secretary
		EASTON CAPITAL PARTNERS, LP
		By:		ECP GP, LLC
		By:		ECP GP, Inc., its Manager
		By:		/s/ Xxxxxxx X. Xxxxxxxxx
				Name: Xxxxxxx X. Xxxxxxxxx
				Title: Vice President and Secretary

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

		MAVERICK FUND, L.D.C.
		By:		Maverick Capital, Ltd.
				Its Investment Advisor
		By:		/s/ Xxxx X. XxXxxxxxxx
				Name: Xxxx X. XxXxxxxxxx
				Title: Limited Partner and General Counsel
		MAVERICK FUND USA, LTD.
		By:		Maverick Capital, Ltd.
				Its Investment Advisor
		By:		/s/ Xxxx X. XxXxxxxxxx
				Name: Xxxx X. XxXxxxxxxx
				Title: Limited Partner and General Counsel
		MAVERICK FUND II, LTD.
		By:		Maverick Capital, Ltd.
				Its Investment Advisor
		By:		/s/ Xxxx X. XxXxxxxxxx
				Name: Xxxx X. XxXxxxxxxx
				Title: Limited Partner and General Counsel

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

		MITSUI & CO. VENTURE PARTNERS II, L.P.
		By:		Mitsui & Co. Venture Partners, Inc.
				Its General Partner
		By:		/s/ Xxxxxx Xxxx
				Name: Xxxxxx Xxxx
				Title: President and CEO

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

	ITX INTERNATIONAL EQUITY CORP.
	By:	/s/ Takehito Jimbo
		Name:	Takehito Jimbo
		Title:	President and CEO

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

	WHITEBOX HEDGED HIGH YIELD PARTNERS, LP
	By:	/s/ Xxxxxxxx Xxxx
		Name:	Xxxxxxxx Xxxx
		Title:	Director and COO

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

	WELLSPRING CAPITAL
	By:	/s/ Xxxxxx Xxxxx
		Name:	Xxxxxx Xxxxx
		Title:	Managing Member

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

	GDN HOLDINGS LLC
	By:	/s/ Xxxx X. Xxxxxx
		Name:
		Title:

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 4 to Investor’s Rights Agreement effective the date first written above.

	SILICON VALLEY BANK
	By:	/s/ Xxxxxxxx Xxxxxxx
		Name:	Xxxxxxxx Xxxxxxx
		Title:	Deal Team Leader