This is a form of dilated cardiomyopathy, meaning the main pumping chamber of the heart stretches, thins and pumps less strongly, caused by a change in a gene called BAG3 that normally helps heart muscle cells clear out damaged proteins [1,3,13].
This page provides general information. It does not replace advice from a doctor or another qualified healthcare professional.
Dilated cardiomyopathy. Cardiomyopathy means a condition of the heart muscle, and dilated means stretched and enlarged. The left ventricle, the chamber that pumps blood to the body, grows larger while its wall thins, so it squeezes less strongly [2,7]. Doctors confirm it when scans show an enlarged left ventricle and an ejection fraction, the share of blood pumped out each beat, below 50 percent, and where nothing else such as a blocked artery, a valve problem or long-standing high blood pressure explains the change [1,4,9]. Alternative names: familial, nonsyndromic and BAG3-related dilated cardiomyopathy [2,9].
How this differs from the hypertrophic form. The two are often confused and are close to opposites: in hypertrophic cardiomyopathy the wall becomes thick and stiff so the heart does not fill easily, while here it becomes thin and stretched so the heart does not squeeze strongly [2,4]. Our guide to MYBPC3-associated non-obstructive hypertrophic cardiomyopathy covers that form.
What the BAG3 gene does. Genes are instructions inside cells, and BAG3 holds the instructions for a protein found mainly in heart and skeletal muscle [13]. Every heartbeat strains heart muscle cells and damages some of their internal proteins. The BAG3 protein helps spot those damaged proteins and route them for repair or clearance, and helps hold the contracting machinery of the cell steady [13,14]. With only one working copy, cells make less than the heart needs, damaged material builds up, and the muscle weakens [13,15].
Dilated cardiomyopathy of all causes may affect as many as 1 in 250 people, and the British Heart Foundation quotes that figure for the United Kingdom [2,7]. That counts people whose scans show the pattern rather than people with a diagnosis, so the diagnosed number is lower [2].
How much of that total BAG3 explains is unsettled. A widely used reference table puts it at about 3 percent and calls that a preliminary estimate [1]. A large European study cites published figures of 2.3 to 3.6 percent across cohorts from the United States, Europe and Japan, and found 6.7 percent at two of its own centers [3]. A separate analysis counting only variants that shorten the protein found them in 0.3 percent of cases [13,15]. The range reflects which variants are counted and which populations and hospitals were studied. Cases occur worldwide, and reliable country-by-country figures are not available [3].
The cause is a change, also called a variant, in the BAG3 gene. Most disease-causing changes stop a working protein being made from that copy, and 86 percent of people in the largest study of affected families carried this type [3,13,15].
Inheritance. It is inherited in an autosomal dominant pattern, meaning one changed copy from one parent is enough. Each child of an affected person has a 1 in 2 chance of inheriting it, and each brother or sister has the same chance [1]. Sometimes the change is new and came from neither parent [1].
Penetrance is the point families most need to understand. Inheriting the change does not mean a person will definitely develop the condition. Doctors call this incomplete penetrance, and for BAG3 it is also age-related, so the chance rises through life [4,11]. In families already known to carry a BAG3 change, around 80 percent of carriers older than 40 had developed the condition, so roughly one in five had not, and the average age at diagnosis was about 37 [3,11].
Two cautions belong with those numbers. Penetrance appears much lower where a BAG3 change is found by chance, through wider testing in someone with no family history of heart disease, than where it is found by testing the relatives of an affected person [12]. For any one individual, no prediction can be made about when the condition might start or how severe it might become [1].
Many people have no symptoms for years, and some are found through family screening while feeling well [1,11]. Common symptoms include [2,7,8]:
Over time some people develop heart failure, meaning the heart cannot keep up with the body’s needs, some develop an irregular rhythm such as atrial fibrillation, and clots can form in the enlarged chamber and cause a stroke [1,7].
When to seek urgent help. Call emergency services for severe breathlessness at rest or breathlessness that wakes you from sleep, severe chest pain, fainting, a fast irregular heartbeat with dizziness, or sudden weakness or drooping on one side of the face or body. If someone collapses and is not breathing normally, start CPR and use a defibrillator if one is nearby.
A cardiologist leads the work-up, ideally at a center that sees inherited heart conditions [4]. An echocardiogram, an ultrasound scan of the heart, is the main test, measuring the size of the left ventricle and how strongly it pumps [1,7]. An electrocardiogram, or ECG, records the heart’s electrical activity, and cardiac MRI gives more detail where the echocardiogram is unclear [1,4,7,8,10].
Genetic testing should be offered to everyone with dilated cardiomyopathy that is not caused by blocked arteries, alongside a conversation with a genetic counselor and a three-generation family history [1,4,16]. It finds a cause in roughly a quarter to 40 percent of people [2,4]. Diagnosis is often delayed, since early symptoms are easy to put down to being unfit.
A genetic diagnosis changes what happens for the whole family, which is the main reason testing is recommended. Once a specific change is confirmed, relatives can be tested for it, and those who do not carry it can usually stop repeat heart checks [4,11].
There is no cure. Treatment protects the heart and eases symptoms, and it is the same treatment used for heart failure with reduced ejection fraction from any cause [4].
Medicines. Standard care rests on four groups of medicine used together: an angiotensin receptor-neprilysin inhibitor or an ACE inhibitor, a beta blocker, a mineralocorticoid receptor antagonist, and an SGLT2 inhibitor, with water tablets to relieve fluid build-up [1,6]. Our guide to heart failure with reduced ejection fraction explains what each group does and how they are started and adjusted.
Defibrillators, and why a genetic cause shifts the conversation. An implantable cardioverter-defibrillator, a small device placed under the skin that can correct a dangerous rhythm, is recommended for anyone who has survived a cardiac arrest and considered where pumping function stays at or below 35 percent despite full medicine treatment [4]. European guidance says the gene should also count: for a few genes linked to high rhythm risk a defibrillator can be considered at better pumping function than that, and BAG3 is not among them [4]. Serious rhythm events with BAG3 ran at about 1 percent per year in the largest study, so knowing the gene shifts the discussion toward watching pumping function rather than earlier implantation [3,11].
Advanced treatment. A heart transplant is recommended where severe symptoms persist despite full treatment, and a left ventricular assist device, a mechanical pump, may be used while waiting for one, though availability and funding differ between countries [4,7].
Family testing and heart checks are the most useful thing to arrange. Parents, brothers, sisters and children should be offered a baseline ECG and heart scan, and genetic testing for the family change where one has been found [10,11]. Relatives who carry the change need repeat checks for life, commonly every one to three years up to about age 60 and every three to five years after that, adjusted for age and earlier findings [4,10]. Relatives who do not carry it can usually be discharged, with advice to return if symptoms appear [4,11]. A single normal check is not a lifetime clearance, since the condition can appear later [4].
Exercise. Regular low to moderate exercise is recommended after an individual review of risk, with around 150 minutes a week as the general target [4,5]. High-intensity and competitive sport are not advised for people with symptoms or with pumping function at or below 40 percent, though everyday activity is fine [4,7].
Pregnancy. Anyone planning a pregnancy should be seen beforehand by a cardiologist and a maternity team, to review their own risk, the 1 in 2 chance of passing the change on, and which medicines must change, since several standard heart failure medicines cannot be used in pregnancy [4]. Pregnancy is not advised where pumping function is very low or symptoms are severe, and a specialist nurse or peer support helps many families through all of this [4,8,11].
Clinical trials test whether a treatment works and is safe. BAG3-associated dilated cardiomyopathy is an active research area, partly because no treatment yet addresses the underlying genetic cause [17]. Looking into a study is a personal choice, and it helps to take it in steps.
Every trial has rules about who can take part, called eligibility criteria. For this condition they might include a confirmed BAG3 gene change reported as pathogenic or likely pathogenic, an ejection fraction inside a set range, being on stable heart failure medicines for a minimum period beforehand, already having an implanted defibrillator, or a blood test showing you have not been exposed to the viral carrier used to deliver a gene therapy.
trialport’s medifit helps people consider information related to possible medical suitability. It does not diagnose a condition, confirm eligibility or replace formal screening by the study team.
Explore BAG3-associated dilated cardiomyopathy clinical trials through trialport
A study can be a good match on paper and still be difficult in practice. Worth thinking through:
trialport’s readifit helps people reflect on their understanding, motivation, time, routines, support, emotions and practical arrangements.
Useful questions to put to a research team:
Taking part is voluntary. A person can ask questions, speak with people they trust and choose not to participate.
Search for clinical trials at app.trialport.com.
Treatments aimed at the gene itself. A gene therapy called RP-A701 is being developed for this condition. It is designed to deliver a working copy of the BAG3 gene to heart muscle cells in a single infusion. The United States Food and Drug Administration cleared it to begin human testing in June 2025, and the company reported in May 2026 that the first person was expected to be treated around the middle of 2026 [17,18]. This is a first-in-human safety study in adults with advanced disease. It is investigational, not approved anywhere, and nothing is yet known about whether it helps.
Gene editing for inherited heart muscle conditions. The British Heart Foundation funds a large international program called CureHeart, working toward treatments that correct the genetic cause of inherited heart muscle conditions, currently at the laboratory stage [19].
Better information for families. Researchers are refining how much risk a BAG3 change carries, which depends heavily on whether it was found through a family or by chance [12].
Study status checked: 3 August 2026. Research moves and what is being studied changes. For current study information, use app.trialport.com.
In the United States, the DCM Foundation supports affected people and families [1,20], the Children’s Cardiomyopathy Foundation offers information, webinars and a parent ambassador program for families of affected children [21], and the American Heart Association explains the condition clearly [9].
In the United Kingdom, Cardiomyopathy UK runs a free specialist nurse helpline, a genetic advice line and an online support group for this condition [8], and the British Heart Foundation covers diagnosis, treatment and daily life and runs a genetic information service [7]. In Australia and New Zealand, Cardiomyopathy Australia New Zealand offers peer support and information sessions [22].
Coverage elsewhere is uneven. The Global Heart Hub Cardiomyopathy Patient Network brings together 35 organizations across 19 countries and is the best starting point [20]. Where no local organization exists, a specialist inherited heart conditions clinic is the next best contact.
If I inherited the BAG3 change, will I definitely develop the condition?
No. Around 80 percent of carriers older than 40 in known families had developed it, so roughly one in five had not, and risk appears considerably lower where the change was found by chance rather than through an affected relative [3,11,12].
Should my children be tested?
Genetic testing and heart checks are recommended for parents, brothers, sisters and children [10,11]. For children the timing is decided with the family and the specialist team, and a genetic counselor talks it through first [4].
How is this different from hypertrophic cardiomyopathy?
Here the muscle stretches, thins and pumps weakly; in the hypertrophic form it thickens, stiffens and does not fill easily [2,4]. Our MYBPC3 hypertrophic cardiomyopathy guide covers that form.
What is the outlook?
The largest study found a demanding course dominated by heart failure rather than rhythm problems: about 30 percent of those affected reached a serious outcome such as transplant, mechanical support or death, roughly 5 percent per year, and outcomes were worse in men [3]. Those figures come from specialist centers, some with large transplant programs, so they may look more severe than average, and the study did not measure what modern treatment changes [3]. Individual outlook cannot be predicted [1].
Is there a cure, and can the heart recover?
There is no cure, and treatment protects the heart and eases symptoms [4,7]. Recovery of pumping function appears less common with BAG3 than with some other genetic causes, which is one reason specialists favor full treatment early [3,13].
Does it affect other muscles?
Usually no. Changes in BAG3 can cause a muscle condition called myofibrillar myopathy, but that is linked to one particular type of change causing a different heart picture, and the large study found no meaningful muscle involvement [3,15].
Written by: trialport editorial team
Reviewed by: Keith Berelowitz, Founder and CEO, trialport
Reviewed on: 3 August 2026
Next review due: 3 August 2027
References last checked: 3 August 2026