Study of the Effect of GS-6615 in Subjects With LQT-3

Inclusion Criteria:

1. Males and females between ages 18-65 years (inclusive) at time of screening

2. Documented LQT-3 genotype with one of the following mutations: delta KPQ, R1623Q,
N1325S, E1784K, S1787N, D1790G, G1631D, 1795insD, delF1617, R1644H, L409P, F2004L,
I1768V, T1304M, A1330T, or F1596I3.

3. QTc > 480 msec in lead V5 at screening

4. Weight of at least 50 kg with body mass index (BMI) between 18 and 30 kg/m^2
(inclusive)

5. Females of childbearing potential must have a negative serum pregnancy test at
screening and check-in

6. Females of childbearing potential must agree to utilize protocol recommended highly
effective contraception methods from three weeks prior to the single dose of study
drug and for 30 days following the single dose of study drug

a. Females who utilize hormonal contraceptive as one of their birth control methods
must have used the same method for at least 3 months prior to study dosing

7. Males must agree to utilize a protocol recommended highly effective method of
contraception during heterosexual intercourse throughout the study period and for 90
days following last dose of study drug. Periodic abstinence and withdrawal are not
acceptable methods of contraception

8. Males must refrain from sperm donation from Day -2 through completion of the study
and continuing for at least 90 days from the date of last dose of study drug

9. Willing and able to comply with the requirements of the protocol and directions from
the clinic staff

10. Willing to avoid consumption of grapefruit, grapefruit juice and Seville oranges
within 2 weeks prior to the single dose of study drug until discharge from the clinic

11. Willing to avoid consumption of nicotine (including nicotine gum) and alcoholic
beverages within 2 weeks prior to the single dose of study drug until discharge from
the clinic

12. Understand and willing to sign informed consent

Exclusion Criteria:

1. Ongoing or history of any medical or surgical condition that, in the judgment of the
Investigator, might jeopardize the individual's safety or interfere with the
absorption, distribution, metabolism or excretion of the study drug

2. History of meningitis or encephalitis, seizures, migraines, tremors, myoclonic jerks,
sleep disorder, anxiety, syncope, head injuries or a family history of seizures

3. Any abnormal electrocardiographic (ECG) findings (except QTc > 460 msec) at screening
judged to be clinically significant by the investigator

4. Any abnormal laboratory value or physical examination finding at screening or
check-in that is judged by the investigator as clinically significant

5. History of positive serology test for HIV, or hepatitis B or C

6. Positive urine drug test for ethanol, barbiturates, cocaine, opiates, or amphetamines
at screening or check-in

7. Positive urine cotinine test at check-in

8. Current treatment with drugs affecting the QT interval

9. Current treatment with sodium-channel blockers, eg, flecainide and mexiletine

10. Current treatment with strong or moderate inhibitors or inducers of cytochrome P450
(CYP)3A4 and 1A2

11. Prior treatment with ranolazine within 7 days prior to study drug administration

12. Use of systemic prescription medications or over-the-counter (OTC) medication,
including multivitamins, and dietary and herbal supplement within 2 weeks or 5 times
the terminal half-lives of the medication (whichever is longer) prior to the single
dose of study drug, and for the duration of the study

13. Use of any experimental or investigational drug or device within 30 days prior to the
single dose of study drug or 5 half-lives of the drug, whichever is longer

14. Females who are pregnant or lactating

15. History of drug or alcohol abuse within 12 months prior to initial dosing of study
drug

16. Psychosocial or addictive disorders that would interfere with ability to give
informed consent or could compromise compliance with the protocol