Description of Securities Registered under Section 12 of the Exchange Act

Exhibit 4.2

DESCRIPTION OF THE REGISTRANT’S SECURITIES

REGISTERED PURSUANT TO SECTION 12 OF THE

SECURITIES EXCHANGE ACT OF 1934

United Therapeutics Corporation (“United Therapeutics”) has one class of securities registered under Section 12 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”): our Common Stock, par value $0.01 per share (our “common stock”).

DESCRIPTION OF COMMON STOCK

The following summary description sets forth some of the general terms and provisions of our common stock. Because this is a summary description, it does not contain all of the information that may be important to you. For a more detailed description of our common stock, you should refer to the provisions of our amended and restated certificate of incorporation, as amended (our “certificate of incorporation”) and our seventh amended and restated bylaws (our “bylaws”), each of which are filed as exhibits to the Annual Report on Form 10-K to which this description is an exhibit.

General

Under our certificate of incorporation, United Therapeutics is authorized to issue up to two hundred forty-five million (245,000,000) shares of our common stock and ten million (10,000,000) shares of preferred stock, par value $.01 per share (our “preferred stock”). The shares of our common stock currently outstanding are fully paid and non-assessable. No shares of preferred stock are currently outstanding. Our board of directors has the authority to make, alter, amend and repeal bylaws in any manner not inconsistent with Delaware law.

No Preemptive, Redemption or Conversion Rights

Our common stock is not redeemable, is not subject to redemption or sinking fund provisions, does not have any conversion rights and is not subject to call. Holders of shares of common stock do not have preemptive rights to acquire newly issued shares.

Voting Rights

Holders of shares of common stock have one vote per share in all elections of directors and on all other matters submitted to a vote of stockholders of United Therapeutics. Holders of shares of common stock do not have cumulative voting rights.

Board of Directors

Our board of directors is divided into three classes as nearly equal in number as the then total number of directors constituting the whole board permits. The term of office of each class expires at the third annual meeting of stockholders for election of directors following the election of such class. At each annual meeting of stockholders, directors of the class whose term then expires are elected to hold office for a term expiring as of the third succeeding annual meeting.

Our certificate of incorporation provides that the number of directors on our board of directors will be fixed by, or in the manner provided in, our bylaws. Our bylaws establish that the number of directors shall be fixed from time to time by our board of directors but shall not be less than five nor more than twenty.

No Action by Stockholder Consent

Our certificate of incorporation prohibits action that is required or permitted to be taken at any annual or special meeting of stockholders of United Therapeutics from being taken by the written consent of stockholders without a meeting.

Power to Call Special Stockholder Meeting

Under Delaware law, a special meeting of stockholders may be called by our board of directors or by any other person authorized to do so in our certificate of incorporation or our bylaws. Our certificate of incorporation provides that special meetings of stockholders may be called only by our board of directors in a resolution approved by a majority of our entire board of directors or by the Chairman of our board of directors, a Vice Chairman of our board of directors or the President of United Therapeutics. At any special meeting of stockholders, only business properly brought before the meeting by or at the direction of the Board of Directors may be conducted.

Advance Notice Provisions

Our bylaws provide that the proposal of business to be considered by stockholders at the annual meeting of stockholders (other than nominations for the election of directors) may be made only if it is (i) specified in the notice of meeting (or any supplement thereto) given by or at the direction of our board of directors or the persons properly calling the meeting, (ii) otherwise properly brought before the meeting by or at the direction of our board of directors, or (iii) properly brought before the meeting by a stockholder who has complied with the advance notice procedures set forth in our bylaws. Our bylaws also provide that nominations for the election of directors may be made by (i) our board of directors or (ii) any stockholder entitled to vote in such election and who has complied with the advance notice procedures set forth in our bylaws.

Proxy Access Nominations

Under our bylaws, a stockholder (or a group of up to 20 stockholders) who has held at least 3% of our common stock for three years or more may nominate director nominees constituting up to 20% of the total number of directors then serving on our board, except that the limit shall be 25%

if fewer than ten directors are then serving on our board, provided that the stockholder(s) and nominee(s) satisfy the requirements specified in our bylaws.

Dividend Rights

Subject to the preferences applicable to any outstanding shares of preferred stock, the holders of common stock are entitled to receive dividends, if any, as and when declared, from time to time, by our board of directors out of funds legally available therefor.

Liquidation, Dissolution or Similar Rights

Upon dissolution, after satisfaction of the claims of creditors and the payment to any holders of preferred stock of the full preferential amounts to which such holders may be entitled, the remaining assets of United Therapeutics would be distributed to the holders of the common stock ratably in proportion to the number of shares of common stock held by them.

Preferred Stock

Under our certificate of incorporation, our board of directors has the authority, without further stockholder action, to issue up to 10 million shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions thereof, including dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting any series and the designation of such series.

Forum Selection Clause

Under our bylaws, unless United Therapeutics consents in writing to the selection of an alternative forum, the sole and exclusive forum for making certain types of claims shall be a state court located within the State of Delaware (or, if no state court located within the State of Delaware has jurisdiction, the federal district court for the District of Delaware). This provision applies to (a) any derivative action or proceeding brought on behalf of United Therapeutics, (b) any action asserting a claim of breach of a fiduciary duty owed by any director, officer or employee of United Therapeutics to United Therapeutics or United Therapeutics’ stockholders, (c) any action asserting a claim arising pursuant to any provision of the General Corporation Law of Delaware (the “DGCL”) or our certificate of incorporation or bylaws, (d) any action asserting a claim governed by the internal affairs doctrine, or (e) any action to interpret, apply, enforce or determine the validity of any provision of our certificate of incorporation or bylaws.

Anti-Takeover Effects of Provisions of our Certificate of Incorporation, Bylaws, and Delaware Law

Various provisions contained in our certificate of incorporation, our bylaws, and Delaware law could delay or discourage some transactions involving an actual or potential change in control of United Therapeutics or its management. For example, under Section 203 of the DGCL, a stockholder holding 15% or more of our outstanding voting stock could not acquire us without consent of our board of directors for at least three years after the date the stockholder first held 15% or more of the voting stock. In addition, our board of directors could, without stockholder approval, implement other anti-takeover defenses, such as a stockholder rights plan.