Alnylam Pharmaceuticals Inc. won expanded US approval for a heart drug that could be the biggest boon yet for the 23-year-old biotech — if it can beat out stiff competition from the likes of Pfizer Inc.

Alnylam’s drug, vutrisiran, was approved for patients with transthyretin amyloid cardiomyopathy, or ATTR-CM, to reduce cardiovascular-related death and hospitalizations. This indication was widely expected among investors and is similar to the indications given for competing therapies.

Amvuttra’s clearance in a rare form of cardiomyopathy could help Alnylam turn a regular profit — if it can wrest control of a competitive and fast-changing market.