UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

x

Rule 13d-1(b)

o

Rule 13d-1(c)

o

Rule 13d-1(d)

CUSIP No. 

1.

Names of Reporting Persons
Tekla Capital Management LLC

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power
811,227

7.

Sole Dispositive Power
811,227

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
811,227

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
6.9%

12.

Type of Reporting Person (See Instructions)
IN

CUSIP No. 

1.

Names of Reporting Persons
Daniel R. Omstead

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

o

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
0

6.

Shared Voting Power
811,227

7.

Sole Dispositive Power
811,227

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
811,227

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
6.9%

12.

Type of Reporting Person (See Instructions)
IN

Item 1.

(a)

Name of Issuer
ARCA biopharma, Inc.

(b)

Address of Issuer’s Principal Executive Offices
11080 CirclePoint Rd, Suite 140, Westminster, CO 80020

Item 2.

(a)

Name of Person Filing
Tekla Capital Management LLC

(b)

Address of Principal Business Office or, if none, Residence
100 Federal Street, 19th Floor, Boston, MA 02110

(c)

Citizenship
Delaware Corporation

(d)

Title of Class of Securities
Common Stock

(e)

CUSIP Number
00211Y407

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

o

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);

(e)

x

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with §240.13d-1(b)(1)(ii)(G);

(h)

o

A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

o

A non-U.S. institution in accordance with § 240.13d–1(b)(1)(ii)(J);

(k)

o

Group, in accordance with § 240.13d–1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with § 240.13d–1(b)(1)(ii)(J), please specify the type of institution:____________________________

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:   

811,227

(b)

Percent of class:   

6.9%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

0

(ii)

Shared power to vote or to direct the vote    

811,227

(iii)

Sole power to dispose or to direct the disposition of   

811,227

(iv)

Shared power to dispose or to direct the disposition of   

0

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   o.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

One person has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Common Stock of ARCA biopharma, Inc.  The interest of Tekla Life Sciences Investors, an investment company registered under the Investment Company Act of 1940, in the Common Stock of ARCA biopharma, Inc. amounted to 811,227 shares or 6.9% of the total outstanding Common Stock at December 31, 2017. 

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

See attached Exhibit A.

Item 8.

Identification and Classification of Members of the Group

Not applicable. 

Item 9.

Notice of Dissolution of Group

N/A

Item 10.

Certification

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

February 12, 2018

Date

/s/ Laura Woodward

Signature

Laura Woodward, Treasurer

Name/Title