Ardelyx (ARDX): RA Capital Management Boosts Stake to 7.7%

CUSIP No. 039697107	13G

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). RA Capital Healthcare Fund, L.P.

	2.	Check the Appropriate Box if a Member of a Group (See Instructions)
		(a)	¨
		(b)	¨

	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	2,451,968
	7.	Sole Dispositive Power	0
	8.	Shared Dispositive Power	2,451,968

 

	9.	Aggregate Amount Beneficially Owned by Each Reporting Person 2,451,968
	10.	Check if the Aggregate Amount in Row (9) Excludes                         ¨ Certain Shares (See Instructions)
	11.	Percent of Class Represented by Amount in Row (9) 5.2%3
	12.	Type of Reporting Person (See Instructions) PN (Limited Partnership)

 

³ The reporting person is the beneficial owner of
2,314,024 shares of Common Stock, as well as warrants to acquire 137,944 shares of Common Stock, which together would constitute
approximately 7.7% of the issuer’s Common Stock if the warrants were exercised in full, following the issuance of 137,944
shares of Common Stock in respect of the fully-exercised warrants. The percentage calculation assumes that there are currently
47,230,378 outstanding shares of the Issuer, based on the Issuer’s 10-Q as filed with the SEC on May 9, 2016 and the Issuer’s
8-K as filed with the SEC on July 20, 2016.