Study of ALXN2220 Versus Placebo in Adults With ATTR-CM

Inclusion Criteria: * Diagnosis of ATTR-CM with either wild-type or variant TTR genotype * End-diastolic interventricular septal wall thickness ≥ 12 mm on echocardiography measured at Screening * NT-proBNP \> 2000 pg/mL at Screening * Treatment with a loop diuretic for at least 30 days prior to Screening * History of heart failure NYHA Class II-IV at Screening * Life expectancy of ≥ 6 months as per the Investigator's judgment * Males and females of childbearing ability must use contraception Exclusion Criteria: * Known leptomeningeal amyloidosis * Known light chain (AL) or secondary amyloidosis (AA), or any other form of systemic amyloidosis * Acute coronary syndrome, unstable angina, stroke, transient ischemic attack, coronary revascularization, cardiac device implantation, cardiac valve repair, or major surgery within 3 months of Screening * Uncontrolled clinically significant cardiac arrhythmia, per Investigator's assessment * LVEF \< 30% on echocardiography * Renal failure requiring dialysis or an eGFR \< 20 mL/min/1.73 m2 at Screening * Polyneuropathy with PND score IV