Atrial fibrillation can and often does lower ejection fraction, the percentage of blood the left ventricle pumps out with each beat. The drop can be modest or dramatic depending on how fast the heart races, how long the arrhythmia persists, and whether the person had underlying heart disease beforehand. In some cases, AF triggers a form of heart muscle weakening severe enough to qualify as heart failure, yet one that is partly or fully reversible once normal rhythm returns. The relationship between AF and ejection fraction is also bidirectional, which makes untangling cause from effect one of the trickier puzzles in cardiology.
Three Ways AF Drags Down Ejection Fraction
The heart normally works as a coordinated pump. The atria contract just before the ventricles, topping off the ventricles with a final surge of blood called the “atrial kick.” In AF, the atria quiver chaotically instead of contracting, and that final top-off disappears. Research in patients with mitral valve narrowing showed that losing the atrial kick reduced both the volume of blood in the left ventricle at the end of filling and the ejection fraction itself, while raising pressures in the left atrium.1The American Journal of Cardiology. Importance of the “atrial kick” in determining the effective mitral valve orifice area in mitral stenosis In a healthy heart the loss of the atrial kick alone may only trim ejection fraction by a few percentage points, but in someone whose heart is already stiff or weakened, even that small deficit matters.
The second mechanism is the irregularity of the heartbeat itself. AF doesn’t just eliminate organized atrial contractions; it also makes the intervals between ventricular beats wildly variable. Even when the average heart rate is kept at a normal level, that beat-to-beat irregularity independently impairs the heart’s pumping ability.2PubMed. Effect of an irregular ventricular rhythm on cardiac output A study in heart-failure patients receiving cardiac resynchronization therapy confirmed this: at faster heart rates, an irregular pacing pattern worsened both the squeezing function and the relaxation function of the left ventricle compared with a perfectly regular rhythm at the same rate.3European Heart Journal. Functional impact of rate irregularity in patients with heart failure and atrial fibrillation receiving cardiac resynchronization therapy The damage from irregularity was negligible at moderate rates but became pronounced once rates climbed, which helps explain why rapid AF is so much more dangerous to the heart muscle than slower AF.
The third and most consequential mechanism is sustained rapid heart rate. When the ventricles beat too fast for too long, the heart muscle gradually weakens, a condition sometimes called arrhythmia-induced cardiomyopathy. This is not a minor curiosity. While stroke remains the most widely feared complication of AF, this form of cardiomyopathy carries substantial illness and death risk of its own.4PubMed Central. Tachycardia and Atrial Fibrillation-Related Cardiomyopathies: Potential Mechanisms and Current Therapies Crucially, the heart muscle damage from prolonged rapid AF tends to be at least partially reversible once the rate or rhythm is brought under control, which sets it apart from many other causes of heart failure.
How Much Ejection Fraction Can Bounce Back
One of the more hopeful aspects of AF-related heart weakness is its potential for recovery. When researchers used an AI model to identify patients whose ejection fraction had dropped during AF but recovered after conversion to a normal rhythm, the average improvement was striking: roughly a 20-percentage-point jump in ejection fraction once sinus rhythm was restored.5PubMed Central. Understanding Transient Left Ventricular Ejection Fraction Reduction During Atrial Fibrillation With Artificial Intelligence That is the difference between a heart that looks like it is in serious trouble and one that looks nearly normal.
Catheter ablation, a procedure that targets the abnormal electrical signals causing AF, has become a key tool for recovering ejection fraction. In a systematic review of patients with AF and reduced pumping function who underwent ablation, about seven in ten were classified as responders, meaning their ejection fraction improved meaningfully.6Arrhythmia & Electrophysiology Review. Predictors of Improvement in Left Ventricular Systolic Dysfunction in Patients with Atrial Fibrillation Undergoing Catheter Ablation: Systematic Review A large European study put a finer point on those numbers: responders saw their ejection fraction climb by about 20 percentage points at one year, while nonresponders barely budged.7European Heart Journal. Left ventricular functional recovery after atrial fibrillation catheter ablation in heart failure: a prediction model Successful ablation can also improve heart-failure symptoms, quality of life, and possibly survival.8PubMed Central. Ablation for Atrial Fibrillation in Heart Failure with Reduced Ejection Fraction
Not everyone responds, though, and the roughly 30% who don’t see much recovery likely have heart muscle damage from causes other than AF itself, such as coronary artery disease or longstanding high blood pressure. Distinguishing someone whose weak heart is caused by AF from someone whose weak heart merely coexists with AF remains one of the harder clinical calls in cardiology. Getting it right matters, because the first person stands to gain enormously from restoring rhythm, while the second may not.
Rhythm Control Versus Rate Control
If you have AF and your ejection fraction has dropped, the big clinical question is whether to try to restore a normal rhythm (rhythm control) or simply slow the heart rate and leave the irregular rhythm in place (rate control). A meta-analysis pooling seven trials found that rhythm-control strategies raised ejection fraction by about four percentage points more than rate-control strategies, though the evidence was considered uncertain because the individual trials were small and their results varied widely.9PLoS ONE. The effects of rhythm control strategies versus rate control strategies for atrial fibrillation and atrial flutter: A systematic review with meta-analysis and Trial Sequential Analysis Four percentage points may not sound like much, but for someone sitting at the edge between adequate and inadequate heart function, it can be the margin that keeps them out of the hospital.
For patients who can’t maintain sinus rhythm and whose rate remains difficult to control, an older “ablate and pace” approach is sometimes used. In that strategy, the electrical bridge between the atria and ventricles is destroyed on purpose and a pacemaker is implanted to keep the ventricles beating at a steady, reasonable rate. Long-term follow-up from the AIRCRAFT trial showed that ejection fraction stayed roughly stable over five years in these patients, though it did drift down modestly, similar to the decline seen in medically managed patients over the same period.10EP Europace. Ablate and pace strategy for atrial fibrillation: long-term outcome of AIRCRAFT trial More recently, pacing the heart through a specific pathway called the His bundle rather than the right ventricle has shown better results: patients with reduced ejection fraction who received His-bundle pacing after ablation of the electrical bridge saw meaningful improvements in both ejection fraction and heart size.11PubMed Central. Benefits of Permanent His Bundle Pacing Combined With Atrioventricular Node Ablation in Atrial Fibrillation Patients With Heart Failure With Both Preserved and Reduced Left Ventricular Ejection Fraction
Why Measuring Ejection Fraction During AF Is Unreliable
Here is something that catches a lot of people off guard: an ejection fraction number obtained while a person is in AF may not reflect their heart’s true pumping ability. Because every beat during AF follows a different-length pause, each beat ejects a different amount of blood. The beat after a long pause fills the ventricle more and pumps harder; the beat after a short pause does the opposite. If the ultrasound technician happens to catch a beat after a long pause, the ejection fraction looks better than average. If they catch one after a short pause, it looks worse.
Research has confirmed that the intervals between the preceding and pre-preceding heartbeats strongly influence stroke volume, and this effect is amplified at faster heart rates.12EP Europace. Is echocardiography valid and reproducible in patients with atrial fibrillation? A systematic review A systematic review examining how reliable echocardiography is in AF patients found that external validation data for systolic function measurements were extremely limited.13PubMed Central. Is echocardiography valid and reproducible in patients with atrial fibrillation? A systematic review In practice, this means clinicians should average several beats rather than relying on a single snapshot, and ideally compare measurements taken during AF with measurements taken after rhythm has been restored. Newer techniques like global longitudinal strain can help detect reduced pumping function even when the standard method is difficult to perform, particularly in AF patients with relatively stable heart rates.14Archives of Cardiovascular Diseases. Can global longitudinal strain predict reduced left ventricular ejection fraction in daily echocardiographic practice?
The Two-Way Street Between Heart Failure and AF
One of the reasons the AF-ejection fraction relationship is so complicated is that it runs in both directions. AF weakens the heart, but a weak heart also promotes AF. When the left ventricle doesn’t pump efficiently, the pressure backs up into the left atrium. That elevated pressure stretches the atrial walls and disrupts the electrical and structural makeup of the atrial tissue, creating the perfect conditions for AF to develop and persist.15PubMed Central. Heart failure with reduced ejection fraction and atrial fibrillation: a Sub‐Saharan African perspective Inflammation and fibrosis are central to this remodeling process, and once the atria have been structurally altered, AF tends to become self-sustaining.
This vicious cycle means that in many patients, both conditions are present by the time they see a doctor, and it is impossible to say which came first. The concept of arrhythmia-induced cardiomyopathy assumes AF caused the heart failure, but there is no definitive blood test or imaging marker that proves the direction of causation. Clinicians often use a trial of rhythm restoration as a diagnostic tool: if ejection fraction bounces back after AF is eliminated, the arrhythmia was likely the primary culprit.
Meanwhile, there is growing recognition that AF and heart failure with a preserved ejection fraction share common underlying problems in the atrial and ventricular muscle, suggesting they sometimes arise together from the same disease process rather than one causing the other.16Circulation. Interdependence of Atrial Fibrillation and Heart Failure With a Preserved Ejection Fraction Reflects a Common Underlying Atrial and Ventricular Myopathy Ventricular fibrosis, the accumulation of scar-like tissue in the heart muscle, appears to contribute to both impaired relaxation and impaired contraction and is a common finding in people with AF.17PubMed Central. Cardiac Fibrosis in Patients With Atrial Fibrillation: Mechanisms and Clinical Implications
What AF Does to the Right Side of the Heart
Most conversations about ejection fraction focus on the left ventricle, the chamber responsible for pumping blood out to the body. But AF also damages the right side of the heart, and this effect is underappreciated. In a study of heart-failure patients whose left-sided ejection fraction was preserved, right ventricular dysfunction was present in about 20% of those who had never had AF, 43% of those with a history of AF, and 63% of those in active AF at the time of assessment. AF was associated with more than a fourfold increase in the odds of right ventricular dysfunction, independent of pressures in the lungs.18PubMed. Right Heart Dysfunction in Heart Failure With Preserved Ejection Fraction: The Impact of Atrial Fibrillation
Even among patients with symptomatic AF and no diagnosed heart failure, roughly one in seven showed evidence of right ventricular dysfunction on echocardiography. Those patients had meaningfully worse exercise capacity, with peak oxygen consumption dropping by nearly three points compared to those with normal right ventricular function.19Heart Rhythm. Right ventricular dysfunction in patients with symptomatic atrial fibrillation: Prevalence and functional implications This matters because standard ejection fraction measurements do not capture right-sided problems at all. A person could have a normal left ventricular ejection fraction but still have significant pumping dysfunction on the right side driven by AF, explaining breathlessness and exercise intolerance that the usual numbers don’t account for.
How AF Affects Prognosis When the Heart Is Already Weak
For patients who already have reduced ejection fraction, developing AF is bad news. A retrospective analysis of the landmark SOLVD trials found that patients with left ventricular dysfunction and AF at baseline had a substantially higher death rate than those in sinus rhythm, around 34% versus 23%. They were also more likely to die from progressive pump failure and more likely to be hospitalized for worsening heart failure. After adjusting for other risk factors, AF remained independently linked to about a 34% higher risk of death.20PubMed. Atrial fibrillation is associated with an increased risk for mortality and heart failure progression in patients with asymptomatic and symptomatic left ventricular systolic dysfunction: a retrospective analysis of the SOLVD trials
Interestingly, when researchers in the Loire Valley project looked at mortality across the full spectrum of ejection fractions in AF patients, they found no significant differences in death rates between those with low, mid-range, and preserved ejection fraction.21European Journal of Heart Failure. Ejection Fraction and Outcomes in Patients with Atrial Fibrillation and Heart Failure: The Loire Valley Atrial Fibrillation Project That might seem contradictory, but it highlights something important: AF itself is the dangerous variable. Once AF is in the picture, even people with a “normal” ejection fraction carry elevated risk, likely because the left-sided number alone doesn’t capture the full burden AF places on the heart through diastolic dysfunction, right-sided impairment, and stroke risk.
Early-Onset AF and Genetic Clues
People who develop AF at a younger age present a distinct picture. A study of early-onset AF patients carrying a specific genetic variant in the titin gene found they had a left ventricular ejection fraction about seven percentage points lower than matched controls, driven not by a larger heart but by a higher volume of blood remaining in the ventricle at the end of contraction. Even early-onset AF patients without this genetic variant had a somewhat reduced ejection fraction compared to controls.22Scientific Reports. Early-onset atrial fibrillation patients show reduced left ventricular ejection fraction and increased atrial fibrosis These findings suggest that in at least some younger AF patients, the arrhythmia and the heart muscle weakness spring from the same genetic soil rather than one causing the other. Recognizing this matters clinically because it means rhythm restoration alone may not fully normalize ejection fraction in patients whose underlying muscle quality is compromised from the start.
Sex Differences in How AF Remodels the Heart
There has long been a clinical sense that AF behaves differently in women and men, and recent research supports this while complicating the picture. A study using direct electrical mapping and tissue samples from inside the atria found that women with AF consistently had lower voltage readings than men, which at first glance suggests more advanced disease in the atrial walls. But when the researchers looked at the actual tissue under the microscope, there were no significant differences in scarring or other pathological changes. The lower voltage in women appears to reflect inherently smaller atrial muscle mass rather than worse disease.23European Heart Journal. Sex differences in atrial fibrillation-related atrial remodelling assessed by electroanatomic mapping and biopsy This is the kind of finding that could change how clinicians interpret electrical data during ablation procedures. Applying the same voltage cutoffs to women and men may lead to overdiagnosing scarring in women, potentially altering treatment decisions without good reason.