With AstraZeneca's ATTR-CM drug failing Phase 3 trials, Pfizer is positioned to capture more of the rare heart disease market.

Pfizer’s tafamidis franchise in transthyretin amyloid cardiomyopathy (ATTR-CM) stands to gain competitive ground after AstraZeneca and Ionis Pharmaceuticals reported a Phase 3 trial failure for their rival drug Wainua on July 9, 2026, removing a major contender from the rare heart disease market.

The late-stage CARDIO-TTRansform trial for Wainua, a gene-silencing therapy, failed to meet its primary efficacy endpoint in ATTR-CM patients, according to reporting from Reuters, CNBC, and Bloomberg. AstraZeneca’s stock fell as much as 9% on the news, and the company lost roughly $27 billion in market value, according to the Wall Street Journal.

ATTR-CM is a rare, progressive, and often fatal heart condition caused by the accumulation of misfolded transthyretin protein in cardiac tissue. AstraZeneca had previously signaled that Wainua represented a significant commercial market opportunity in this segment, according to TechTimes reporting. The global ATTR-CM market reached $5.85 billion in 2025 and is expected to reach $64.09 billion by 2033, according to DataM Intelligence.

With Wainua’s failure, Pfizer’s tafamidis products—sold under the brand names Vyndaqel, Vyndamax, and Vynmac—face reduced near-term competitive pressure. Pfizer’s tafamidis franchise generated $1.7 billion in worldwide sales in 2025, according to company earnings reports. The drugs work by stabilizing the misfolded transthyretin protein, preventing it from clumping in the heart.

According to a Simply Wall St analysis published in Yahoo Finance, Pfizer’s late-stage rare-disease portfolio can contribute to long-term resilience by reducing near-term competitive pressure around ATTR-CM. The analysis noted that “a cleaner competitive field in a rare cardiomyopathy indication supports the idea that selected existing assets, rather than only future partnerships or acquisitions, can carry more of the load in rare disease revenue.”

The failure simplifies the ATTR-CM landscape for prescribers, according to BioSpace reporting. Mizuho Securities noted that Wainua’s failure “simplifies the ATTR-CM landscape,” potentially directing more patients toward established therapies. However, Pfizer still faces competition from other approved and pipeline candidates. BridgeBio’s Attruby, approved in November 2024, is also a TTR stabilizer and brought in $362.4 million in 2025. Alnylam’s Amvuttra, an RNA interference therapy, reached approximately 1,400 patients and generated more than $490 million in its first commercial quarter for ATTR-CM, according to BioSpace.

Analysts are watching how quickly cardiologists update prescribing patterns following the Wainua failure and whether Pfizer discloses changes in Vyndamax volumes or pricing in upcoming earnings reports. The setback for AstraZeneca and Ionis may also affect investor confidence in other TTR-silencing therapies in development, including Alnylam’s next-generation candidate nucresiran, which is in Phase 3 testing.