The aim of this study is to assess the safety and efficacy of varying doses of ISIS 301012 (mipomersen) as add-on therapy in subjects with Heterozygous Familial Hypercholesterolemia

Inclusion Criteria:

• Weight ≥ 50 kg
• Diagnosis of Heterozygous Familial Hypercholesterolemia.
• Females must be non-pregnant and non-lactating.
• On stable lipid lowering therapy for at least 4 weeks.
• Lipid levels meet the pre-specified criteria.

Exclusion Criteria:

• Subject had heart problems in the prior 6 months.
• Subject has elevated ALT, AST, or CPK.
• History of renal disease, liver disease, or malignancy.
• Use of oral anticoagulants, unless the dose has been stable for 4 weeks
• Have any other conditions, which in the opinion of the Investigator would make the subject unsuitable for enrollment, or could interfere with the subject participating in or completing the study.