The Heart Drug That Should Have Worked — But Didn't

Why Nerves Aren't Hearts

This failure challenges a core assumption that had been floating around the ATTR world: if you can silence the TTR gene to fix nerve damage, you should be able to fix heart damage too. It's the same bad protein, right?

Not so fast. Peripheral nerves are relatively forgiving. They have functional reserve, and when you remove the toxic stimulus, surviving nerve fibers can recover. Hearts, on the other hand, are stubborn organs. Once amyloid protein infiltrates heart muscle, the damage tends to stick around. The tissue stiffens, the walls thicken, and regeneration is extremely limited.

There's a population difference too. Nerve disease (ATTRv polyneuropathy) tends to hit younger patients with a specific genetic mutation. Heart disease includes a huge chunk of older "wild-type" patients whose ATTR-CM is age-related, not gene-driven. These patients carry more comorbidities and competing health risks, which makes it much harder for any single drug to move the needle on hard outcomes like death and hospitalization.

Alnylam's vutrisiran (Amvuttra) actually did pull this off in its HELIOS-B trial, reducing cardiovascular death and heart failure events by about 28% overall. But the comparison raises a tricky question: was it the drug, the trial design, or the patient mix that made the difference?

Winners, Losers, and the Reshuffled Deck

Wall Street moved fast. Ionis fell 21–24%, wiping out a major pillar of its growth story. Analysts across the board slashed price targets: Jefferies cut from $113 to $90, BofA from $111 to $90, and Oppenheimer from $110 to $92. Most kept their Buy ratings, though, signaling that the damage is painful but not fatal for a company with a broader RNA platform.

AstraZeneca's drop was steeper (8–13%) because of the surprise nature of the failure. Jefferies analyst Michael Leuchten framed the bigger issue as a "credibility loss" given how confident management had been heading into the readout. Morningstar didn't even change its fair value estimate for AstraZeneca.

The real winners? Alnylam and BridgeBio. With one fewer credible competitor in ATTR-CM, both companies saw their positions strengthen overnight. BridgeBio's Attruby (acoramidis), a next-generation stabilizer approved in late 2024, jumped roughly 15%. Alnylam's Amvuttra now stands as potentially the only approved RNA silencer for ATTR-CM, a massive competitive moat.

A $6 Billion Market With Fewer Contestants

The ATTR-CM market is currently worth an estimated $6–7 billion globally and could double or more by 2030 as diagnosis rates climb. Pfizer dominates with about 75–80% share through tafamidis.

Eplontersen's failure simplifies the landscape. Stabilizers (tafamidis, acoramidis) remain the backbone of treatment, especially for patients with predominantly cardiac disease. Silencers retain a role, but Alnylam's vutrisiran is now the clear leader in that category, particularly for patients who have both nerve and heart involvement.

The UK's health technology body, NICE, has already recommended all three frontrunners (tafamidis, acoramidis, vutrisiran) for cardiomyopathy, with explicit guidance to prescribe the cheapest stabilizer available. That pricing pressure, combined with eplontersen's exit, means Pfizer, BridgeBio, and Alnylam are now fighting a three-way war with one fewer distraction.

What Happens Next

AstraZeneca and Ionis plan to present the full CARDIO-TTRansform dataset at the European Society of Cardiology (ESC) Congress in August 2026. But analysts are skeptical that fuller data will change the story.

For Ionis, the setback removes a potentially multi-billion-dollar revenue stream from its cardiac franchise. The company still has its approved polyneuropathy indication and a deep RNA pipeline, but Wall Street had been pricing in a cardiac blockbuster. That premium just evaporated.

The deeper lesson here might be about humility. Biology doesn't always generalize the way we'd like. A drug that rescues nerves won't necessarily save hearts. And a trial designed to test a therapy on top of an already effective treatment will sometimes prove that the existing treatment was good enough all along.

Sometimes acing the midterm doesn't guarantee the final.

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