Myqorzo nHCM Phase 3: Efficacy Signal Real, But Heart Failure Imbalance Opens Regulatory and Payer Fault Lines

Myqorzo Phase 3 Data Reinforces Efficacy, Raises Safety Questions

Cytokinetics presented detailed Phase 3 data for its drug Myqorzo in non-obstructive hypertrophic cardiomyopathy (HCM) at the European Society of Cardiology (ESC) 2026 meeting, with findings also published in The New England Journal of Medicine. The study showed Myqorzo led to an average 11.4-point improvement on a heart health questionnaire after 36 weeks, compared to 8.4 points for placebo, and improved peak oxygen consumption. Despite these robust efficacy results, Cytokinetics' shares dropped over 7% following the disclosure of 10 Myqorzo-treated patients experiencing a specific type of heart failure versus three in the placebo group. Analysts, however, largely maintained a positive outlook, citing the overall strong efficacy and the absence of deaths in the Myqorzo arm compared to three in the placebo group.

• Detailed Phase 3 data for Myqorzo, presented at ESC 2026 and published in The New England Journal of Medicine, reinforced the drug's efficacy in non-obstructive hypertrophic cardiomyopathy. Patients receiving Myqorzo demonstrated an average 11.4-point improvement on a heart health questionnaire after 36 weeks, significantly better than the 8.4-point change observed in placebo recipients. Additionally, peak oxygen consumption improved in the Myqorzo group while slightly declining in the placebo group, with effects consistent across all analyzed study groups and appearing to grow over time.
• Despite the positive efficacy, Cytokinetics' stock fell over 7% following the disclosure of a safety concern in the detailed data. The paper revealed that 10 patients treated with Myqorzo experienced a specific kind of heart failure, compared to only three patients in the placebo arm. This finding is expected to intensify an ongoing debate regarding the safety profile of Myqorzo and similar drugs for non-obstructive HCM, a condition affecting about one-third of HCM patients.
• Analysts largely viewed the stock sell-off as an overreaction, emphasizing the overall robust efficacy data and the critical unmet need for non-obstructive HCM patients who currently have limited treatment options. Notably, there were no deaths among Myqorzo-treated patients, whereas three deaths occurred in the placebo arm. Experts believe the comprehensive evidence should still support a new approval for Myqorzo and lead to broader clinical adoption, despite the identified safety signal.

Myqorzo's Phase 3 Data: Efficacy and Safety in Non-obstructive HCM

The MAVERICK-HCM trial evaluated mavacamten in non-obstructive HCM using pharmacokinetic-adjusted dosing targeting plasma concentrations of 200 or 500 ng/mL. On the efficacy front, the pooled mavacamten group demonstrated a 53% reduction in NT-proBNP geometric mean versus 1% with placebo, alongside a 34% decrease in cardiac troponin I geometric mean compared to a 4% increase in the placebo arm (p = 0.009). From a safety perspective, serious adverse events were reported in 10% of mavacamten-treated participants versus 21% on placebo; notably, five participants experienced reversible reductions in LVEF to ≤45%, underscoring the need for cardiac function monitoring with this agent.

The FOREST-HCM trial assessed aficamten (initiated at 5 mg daily, titrated in 5 mg increments up to 20 mg based on LVEF) over a 36-week period in non-obstructive HCM patients. Efficacy outcomes were broadly positive: 79.4% of patients achieved ≥1 NYHA class improvement, the Kansas City Cardiomyopathy Questionnaire clinical summary score improved by a mean of 13.8 ± 12.5 points, and median NT-proBNP declined significantly from baseline (−665.5 pg/mL; p < 0.0001). High-sensitivity cardiac troponin I remained unchanged (p = 0.25), and LVEF showed a modest but statistically significant reduction of −4.3% ± 5.2 from a baseline of 70% ± 6.1 (p < 0.0001). The safety profile was favorable, with no drug discontinuations due to adverse events and LVEF falling below 50% in only 2 patients (5.9%).

A randomized triple-crossover trial comparing bisoprolol (target dose 7.5 mg) and verapamil (target dose 360 mg) against placebo provided important context for conventional pharmacotherapy in non-obstructive HCM. Neither agent improved peak oxygen consumption (pVO2) over placebo — in fact, bisoprolol was associated with a statistically significant reduction in pVO2 of −2.5 mL/kg/min versus placebo (P = 0.002), while verapamil showed no significant difference (−0.7 mL/kg/min; P = 0.990). Verapamil did demonstrate favorable effects on global longitudinal strain (−1.1%; P = 0.001) and NT-proBNP (−177 ng/L; P < 0.001), whereas bisoprolol worsened NT-proBNP (+165 ng/L; P = 0.006) and Kansas City Cardiomyopathy Questionnaire Overall Summary Score (−6.6 points; P = 0.001). Safety signals with bisoprolol included increased left atrial volume index (+13.0 mL/m²; P < 0.001) and elevated tricuspid regurgitation pressure gradient (+4.3 mmHg; P = 0.049), with NYHA functional class remaining unchanged across both active treatment arms.

Addressing the Unmet Need in Non-obstructive HCM

Non-obstructive hypertrophic cardiomyopathy (HCM) presents a distinct therapeutic challenge, historically managed with agents borrowed from obstructive HCM protocols despite a near-total absence of robust randomized evidence supporting their use. Recent trial data have not only failed to confirm benefit from standard pharmacotherapy but have, in several cases, demonstrated measurable harm — reframing the unmet need in this population as both clinical and evidentiary.

• Absence of a robust evidence base: Randomized evidence supporting beta-blockers and calcium antagonists in non-obstructive HCM has been absent until recently, meaning clinical practice has long proceeded without rigorous trial-level validation. A randomized triple-crossover trial comparing bisoprolol and verapamil represents one of the first structured attempts to address this gap.

• Beta-blocker therapy worsens key outcomes: Bisoprolol at a target dose of 7.5 mg reduced peak oxygen consumption (pVO2) by −2.5 mL/kg/min versus placebo (P = 0.002), decreased KCCQ Overall Summary Score by −6.6 points (P = 0.001), increased NT-proBNP by +165 ng/L (P = 0.006), increased left atrial volume index by +13.0 mL/m² (P < 0.001), and elevated tricuspid regurgitation pressure gradient by +4.3 mmHg (P = 0.049) — indicating deterioration across symptomatic, biomarker, and structural domains.

• Chronotropic incompetence compounds rate-limiting therapy: Chronotropic incompetence was present in 50% of studied HCM patients, with heart rate reserve identified as an independent predictor of exercise capacity (R² = 76.7%). Both bisoprolol (−37 bpm; P < 0.001) and verapamil (−17 bpm; P < 0.001) reduced peak heart rate versus placebo, risking further impairment of exercise capacity in a population already prone to blunted heart rate response.

• Verapamil provides neither harm nor meaningful benefit: Although verapamil at 360 mg did not reduce pVO2 compared with placebo (adjusted mean difference −0.7 mL/kg/min; P = 0.990), it similarly failed to improve exercise capacity, anaerobic threshold oxygen consumption, VE/VCO₂ slope, or NYHA functional classification — offering no therapeutic gain.

• Hemodynamic and functional abnormalities are underestimated by standard assessment: Resting cardiopulmonary exercise testing variables correlate only modestly with hemodynamics in non-obstructive HCM (r = 0.33–0.51). Pulmonary capillary wedge pressure elevations (≥15 mmHg) were detected in 22% of non-obstructive HCM subjects and pulmonary artery systolic pressure elevations (≥30 mmHg) in 33%, suggesting that routine assessments systematically underappreciate the hemodynamic burden.

• Diastolic dysfunction and myocardial fibrosis lack targeted pharmacotherapy: Diastolic dysfunction — more severe in patients with myocardial fibrosis — is a central pathophysiologic driver in non-obstructive HCM, yet no approved agent directly addresses abnormal myocardial relaxation or the downstream consequences of increased chamber stiffness and impaired diastolic filling.

• Emerging targeted therapies remain nascent: Cardiac myosin modulators, including mavacamten and aficamten, offer mechanistically directed approaches by modulating myosin-actin interactions, with promising early clinical trial results. Gene therapy holds potential to address the underlying genetic etiology, but both modalities remain investigational and are not yet established as standard of care in non-obstructive HCM.

• Invasive options carry significant procedural trade-offs: For medically refractory patients, alcohol septal ablation (ASA) carries more than twice the risk of permanent pacemaker implantation compared with surgical myectomy (10% vs. 4.4%; P < 0.001) and a fivefold higher risk of reintervention (7.7% vs. 1.6%; P = 0.001), limiting the appeal of procedural escalation in this population.

Myqorzo's Position in the Evolving Non-obstructive HCM Landscape

Non-obstructive hypertrophic cardiomyopathy (nHCM) presents a distinct therapeutic challenge, with pharmacological options largely confined to symptomatic management. Cardiac myosin inhibitors (CMIs) — specifically mavacamten — have been evaluated as investigational therapies in this population through randomized controlled trials (RCTs). The ODYSSEY-HCM trial, the largest trial to date assessing mavacamten in symptomatic adults with nHCM, failed to demonstrate improvements in its primary endpoints of functional capacity and patient-reported health status. A systematic review and meta-analysis of two RCTs (n = 639) corroborated these findings, showing no statistically significant pooled differences in KCCQ score (MD: 2.12; 95% CI: −0.98 to 5.22), peak oxygen consumption (MD: 0.36 mL/kg/min; 95% CI: −0.20 to 0.92), or NYHA class improvement (RR: 1.15; 95% CI: 0.93 to 1.43) versus placebo. A separate phenotype-stratified meta-analysis further identified a suggestive worsening in KCCQ-CSS among nHCM patients treated with mavacamten (MD −0.70; 95% CI: −1.26 to −0.14), reinforcing the absence of functional benefit in this subpopulation.

Notwithstanding the lack of functional improvement, mavacamten exhibited pronounced biological activity in nHCM. At week 48 in the ODYSSEY-HCM trial, the mavacamten group demonstrated a 58% reduction in NT-proBNP (geometric mean ratio: 0.42; 95% CI: 0.37–0.47; P < 0.001) and a 51% reduction in hs-cTnI (geometric mean ratio: 0.49; 95% CI: 0.45–0.53; P < 0.001), with no significant change observed in the placebo group. These reductions emerged early and were sustained through week 48. Secondary analyses also revealed favourable effects on left ventricular diastolic function and hypertrophy parameters, though whether these translate into longer-term adaptive remodelling or meaningful improvements in exercise capacity and clinical outcomes remains to be established.

A critical safety signal distinguishes nHCM from obstructive HCM (oHCM) in the context of CMI use. The risk of left ventricular ejection fraction declining below 50% was markedly elevated in nHCM patients treated with mavacamten (OR 14.35; 95% CI: 5.92–34.77), compared with no significantly elevated risk in oHCM (OR 2.08; 95% CI: 0.79–5.48), though this finding warrants cautious interpretation given the limited number of events. Atrial fibrillation also occurred more frequently with mavacamten in nHCM (RR: 1.41; 95% CI: 1.28–1.56), whereas palpitations and dizziness did not differ significantly between treatment groups. This divergent benefit-risk profile between phenotypes underscores the importance of phenotype-guided precision therapy, stringent echocardiographic surveillance, and careful consideration of the implications of off-label CMI use in non-obstructive disease.

Myqorzo's Non-Obstructive HCM Data: A Complex Advance

Hypertrophic cardiomyopathy (HCM) is a complex genetic heart condition characterized by myocardial hypercontractility, which can lead to debilitating symptoms and significant morbidity. While cardiac myosin inhibitors (CMIs) have revolutionized the treatment of obstructive HCM (oHCM) by directly targeting the underlying pathophysiology, non-obstructive HCM (nHCM) has remained a challenging area with limited disease-specific therapies. Previous attempts with CMIs in nHCM have not consistently met primary endpoints, underscoring the difficulty in demonstrating clear benefits in this population.

Against this backdrop, Myqorzo's Phase 3 data in nHCM, showing improvements in heart health questionnaire scores and peak oxygen consumption, represents a notable advance. These efficacy results suggest that Myqorzo could offer a much-needed therapeutic option for nHCM patients, potentially improving their functional status and quality of life. This could expand the utility of the CMI class beyond oHCM, opening a new market segment and validating the mechanism in a broader spectrum of HCM.

However, the positive efficacy is tempered by a safety signal: an increased incidence of heart failure events in the Myqorzo arm compared to placebo. This finding is critical and will necessitate careful consideration during regulatory review and by clinicians. While CMIs are known to reduce left ventricular ejection fraction (LVEF), requiring vigilant monitoring and dose adjustments, the specific increase in heart failure events warrants close attention. The drug's long-term safety and the precise mechanisms contributing to these events will be crucial for its adoption. Moving forward, the balance between Myqorzo's demonstrated efficacy in nHCM and its safety profile will define its role in the evolving landscape of HCM management, potentially establishing it as a valuable, albeit carefully managed, treatment option.