Inclusion Criteria: 

• Subjects with HAE Type I or II who either have participated in a previous BCX7353 study or, in selected countries, in the opinion of the Investigator are expected to derive benefit from an oral treatment for the prevention of angioedema attacks. 
• Access to appropriate medication for treatment of acute attacks.
• Acceptable effective contraception.
• Written informed consent.

Exclusion Criteria: 

• Pregnancy or breast-feeding.
• Any clinically significant medical condition or medical history that, in the opinion of the Investigator or Sponsor, would interfere with the subject's safety or ability to participate in the study.
• Any laboratory parameter abnormality that, in the opinion of the Investigator, is clinically significant and relevant for this study.
• Discontinuation of study drug due to a hypersensitivity reaction BCX7353 in a prior study.
• Severe hypersensitivity to multiple medicinal products or severe hypersensitivity/ anaphylaxis with unclear etiology.
• Unacceptable noncompliance in a previous BCX7353 study (if applicable) as assessed by the Sponsor or Investigator.
• Investigational drug exposure, other than BCX7353, within 30 days prior to the screening visit (or baseline if no screening visit).