Sec Form 3 Filing - FirstMark Horizon Sponsor LLC @ FirstMark Horizon Acquisition Corp. - 2020-10-05

FORM 3 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 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 FirstMark Horizon Sponsor LLC 2. Issuer Name and Ticker or Trading Symbol FirstMark Horizon Acquisition Corp. [ FMAC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 100 5TH AVE, 3RD FLOOR, 3. Date of Earliest Transaction (MM/DD/YY) 10/05/2020 (Street) NEW YORK,, NY10011 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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 (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 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 Class B common stock ( 1 ) ( 1 ) ( 1 ) Class A common stock 8,505,000 D ( 2 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other FirstMark Horizon Sponsor LLC 100 5TH AVE, 3RD FLOOR NEW YORK,, NY10011 X X HEITZMANN RICHARD R C/O FIRSTMARK HORIZON ACQUISITION CORP. 100 5TH AVE, 3RD FLOOR NEW YORK,, NY10011 X CEO JANI AMISH A C/O FIRSTMARK HORIZON ACQUISITION CORP. 100 5TH AVE, 3RD FLOOR NEW YORK,, NY10011 X President Signatures /s/ FirstMark Horizon Sponsor LLC 10/05/2020 Signature of Reporting Person Date /s/ Richard Heitzmann 10/05/2020 Signature of Reporting Person Date /s/ Amish Jani 10/05/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )As described in the issuer's registration statement on Form S-1 (File No. 333-248916) under the heading "Description of Securities--Founder Shares," the shares of Class B common stock, par value $0.0001 per share, of the issuer will automatically convert into shares of Class A common stock, par value $0.0001 per share, of the issuer at the time of the issuer's initial business combination, or earlier at the option of the holder, on a one-for-one basis, subject to certain adjustment, and have no expiration date. Includes 1,125,000 shares of Class B common stock that are subject to forfeiture if the underwriter of the issuer's initial public offering does not exercise in full its option to purchase additional units. ( 2 )The reporting owner, FirstMark Horizon Sponsor LLC (the "Sponsor"), in whose name the securities reported herein are held, is managed by its managers, Richard Heitzmann and Amish Jani. Messrs. Heitzmann and Jani may be deemed to beneficially own shares held by the Sponsor by virtue of their shared control over the Sponsor. Each of Messrs. Heitzmann and Jani disclaims beneficial ownership of the shares held by the Sponsor, except to the extent of such person's pecuniary interest therein.

Remarks: Exhibit 24.1 - Powers of Attorney. Messrs. Heitzmann and Jani, the managers of the Sponsor, serve on the board of directors of the issuer. For the purposes of Section 16 of the Securities Exchange Act of 1934, as amended, the Sponsor may be deemed a director by deputization with respect to the issuer on the basis of the service of Messrs. Heitzmann and Jani on the issuer's board of directors.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* 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).

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