Study of Plozasiran (ARO-APOC3) in Adults With Mixed Dyslipidemia

Key Inclusion Criteria: Based on medical history, prior evidence of triglycerides (TG) ≥ 150 milligrams (mg)/deciliter (dL) and ≤ 499 mg/dL * Fasting levels at Screening of non-high-density lipoprotein cholesterol (non-HDL-C) ≥ 100 mg/dL or low-density lipoprotein cholesterol (LDL-C) ≥ 70 mg/dL after at least 2 weeks of stable diet and 4 weeks on stable optimal statin therapy * Mean fasting TG ≥ 150 mg/dL and ≤ 499 mg/dL during Screening collected at two separate and consecutive visits and at least 7 days apart and not more than 17 days apart * Willing to follow diet counseling as per Investigator judgment based on local standard of care * Participants of childbearing potential (males \& females) must use highly effective contraception during the study and for at least 24 weeks following the last dose of study medication. Males must not donate sperm and females must not donate eggs during the study and for at least 24 weeks following the last dose of study medication. * Women of childbearing potential must have a negative pregnancy test at Screening and cannot be breastfeeding * Women of childbearing potential on hormonal contraceptives must be stable on the medication for ≥ 2 menstrual cycles prior to Day 1 * Willing to provide written informed consent and to comply with study requirements Key Exclusion Criteria: * Current use or use within 365 days from Day 1 of any hepatocyte targeted short interfering RNA oligonucleotides (siRNA) or antisense oligonucleotide molecule * Active pancreatitis within 12 weeks prior to Day 1 * Any planned bariatric surgery or similar procedures to induce weight loss from consent through end of study * Acute coronary syndrome event within 24 weeks of Day 1 * History of major surgery within 12 weeks of Day 1 or planned major surgery during the study * Planned coronary intervention (such as, stent placement or heart bypass) during the study * New York Heart Association (NYHA) Class II, III or IV heart failure or last known ejection fraction of \<30% * Uncontrolled hypertension * Known history of human immunodeficiency virus (HIV) infection, seropositive for Hepatitis B virus (HBV), seropositive for Hepatitis C virus (HCV) * Uncontrolled hypothyroidism or hyperthyroidism * Hemorrhagic stroke within 24 weeks of Day 1 * History of bleeding diathesis or coagulopathy * Current diagnosis of nephrotic syndrome * Systemic use of corticosteroids or anabolic steroids within 4 weeks prior to Day 1 or planned use during the study * Malignancy within the last 2 years prior to date of consent requiring systemic treatment (some exceptions apply) Note: Additional inclusion/exclusion criteria may apply per protocol