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PubMed This is a summary of 20 peer-reviewed journal articles Updated
Cardiology · Arrhythmogenic Cardiomyopathy

Signs, Symptoms, and Warning Signs of ACM

At a Glance

Arrhythmogenic Cardiomyopathy (ACM) is a hidden heart condition that can be present without symptoms for years. When warning signs do appear, they often include a racing heart, lightheadedness, and fainting, particularly triggered by high-intensity exercise or stress.

Arrhythmogenic Cardiomyopathy (ACM) is often called a “hidden” condition because it can exist in the body for years without causing a single noticeable symptom [1][2]. When symptoms do appear, they often mimic other, more common issues, which is why understanding the specific warning signs of ACM is vital for your safety.

Common Signs and Symptoms

For many patients, the first signs of ACM are related to arrhythmias (irregular heart rhythms). These occur because the scar tissue in the heart disrupts the normal electrical flow [3][4].

  • Palpitations: A feeling that your heart is skipping a beat, fluttering, or racing [3][5].
  • Syncope (Fainting): Unexplained loss of consciousness, particularly if it happens during or right after physical activity, is a major warning sign [4][6].
  • Lightheadedness: Feeling dizzy or “graying out” during exertion [6].
  • Shortness of Breath: Difficulty breathing that feels out of proportion to the activity you are doing [7].
  • Chest Pain: Discomfort or pressure in the chest, which can sometimes be mistaken for a heart attack or muscle strain [3][8].

The ‘Hot Phase’: A Myocarditis Mimic

Some patients, particularly those with a specific genetic mutation called DSP (desmoplakin), may experience what doctors call a “hot phase” [9][10]. This is an active period of inflammation in the heart muscle [11][8].

During a hot phase, you might experience:

  • Intense chest pain [8][7].
  • Elevated levels of troponin (a protein released when heart cells are damaged), which is the same marker doctors look for during a heart attack [7][12].
  • Flu-like symptoms or extreme fatigue [7].

These episodes often look exactly like myocarditis (inflammation of the heart usually caused by a virus) [8][11]. If you have been diagnosed with “recurrent myocarditis,” it is often a clue for doctors to look closer at a potential ACM diagnosis [10][9].

Why Can it Stay Hidden? (The Concealed Phase)

ACM often begins with a concealed phase. During this time, the “glue” between your heart cells is weakening at a microscopic level, but the heart still looks normal on standard tests like an ultrasound (echocardiogram) [1][2].

Because the heart’s structure hasn’t changed yet, you may feel perfectly fine [2]. However, even in this hidden stage, the electrical system can be unstable, meaning that sudden cardiac events can occasionally be the very first symptom a person experiences [4][13]. This is why cascade screening—testing the family members of a person with ACM—is so critical [1].

Triggers: The Role of Exercise and Stress

Symptoms of ACM are frequently “dose-dependent,” meaning they are often triggered by high-intensity activity [14][15].

  • Adrenergic Stress: When you exercise or experience high stress, your body releases adrenaline. In ACM, the heart cells are extra sensitive to this adrenaline, which can trigger dangerous heart rhythms [16][17].
  • Mechanical Strain: Vigorous movement physically pulls on the weakened heart cell connections, which can trigger symptoms or cause a “hot phase” to begin [18][19].

If you notice that your heart “flutters” or you feel dizzy specifically during exercise, it is important to stop the activity and consult your cardiologist [14][20].

Common questions in this guide

What are the first signs of arrhythmogenic cardiomyopathy (ACM)?
The earliest signs of ACM are usually related to irregular heart rhythms. You may experience palpitations, a racing heart, lightheadedness, or sudden fainting, especially during or right after physical activity.
Can I have ACM without experiencing any symptoms?
Yes. ACM often begins with a concealed phase where the heart's structure appears normal on an ultrasound and you feel perfectly fine. However, the electrical system can still be unstable, which is why screening family members of diagnosed patients is crucial.
What does a 'hot phase' mean in ACM?
A hot phase is an active period of heart inflammation that mimics a viral infection like myocarditis. It can cause intense chest pain, flu-like symptoms, and elevated troponin levels. This is especially common in patients with a specific genetic mutation called DSP.
Why does exercise trigger ACM symptoms?
High-intensity exercise releases adrenaline and puts physical strain on the heart muscle. In ACM, the weakened connections between heart cells are highly sensitive to this stress, which can trigger dangerous arrhythmias or bring on an active phase of inflammation.
Is it normal to have chest pain with ACM?
Chest pain can occur, particularly during a hot phase of active inflammation in the heart muscle. Because this pain can feel similar to a heart attack or severe muscle strain, it should always be evaluated immediately by a medical professional.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Could the episodes of palpitations or lightheadedness I'm feeling be exercise-induced arrhythmias?
  2. 2.Have my tests shown any signs of a 'hot phase' or recent inflammation in my heart muscle?
  3. 3.Is the chest pain I'm experiencing typical for ACM, or could it be something else like myocarditis?
  4. 4.If I have been asymptomatic, what specific tests (like an ECG or Holter monitor) will we use to track if the disease is progressing?
  5. 5.Are there specific 'red flag' symptoms I should go to the emergency room for immediately?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (20)
  1. 1

    High penetrance and similar disease progression in probands and in family members with arrhythmogenic cardiomyopathy.

    Chivulescu M, Lie ØH, Popescu BA, et al.

    European heart journal 2020; (41(14)):1401-1410 doi:10.1093/eurheartj/ehz570.

    PMID: 31504415
  2. 2

    Arrhythmogenic cardiomyopathy: pathogenesis, pro-arrhythmic remodelling, and novel approaches for risk stratification and therapy.

    van der Voorn SM, Te Riele ASJM, Basso C, et al.

    Cardiovascular research 2020; (116(9)):1571-1584 doi:10.1093/cvr/cvaa084.

    PMID: 32246823
  3. 3

    Ventricular predominance in biventricular arrhythmogenic cardiomyopathy: Should new subtype criteria be recognized?

    Luna-Alcala S, Garcia-Cardenas M, Guerra EC, et al.

    Radiology case reports 2024; (19(6)):2457-2463 doi:10.1016/j.radcr.2024.03.014.

    PMID: 38585407
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    What's New in Arrhythmogenic Cardiomyopathies.

    Çimen T, Saguner AM

    Journal of clinical medicine 2022; (11(16)) doi:10.3390/jcm11164764.

    PMID: 36013003
  5. 5

    Recurrent Syncope in a Patient With Arrhythmogenic Right Ventricular Cardiomyopathy.

    Castillo E

    Cureus 2023; (15(9)):e45850 doi:10.7759/cureus.45850.

    PMID: 37881382
  6. 6

    Comparison of CMR Findings according to the Presence or Absence of Isolated Focal Right Ventricular Dyskinetic Segments in Patients with Clinical Suspicion of ARVC.

    Ko SM

    Journal of cardiovascular imaging 2019; (27(2)):102-104 doi:10.4250/jcvi.2019.27.e24.

    PMID: 30993944
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    Inflammation-A Possible Link between Myocarditis and Arrhythmogenic Cardiomyopathy.

    Lala IR, Pop-Moldovan A

    Diagnostics (Basel, Switzerland) 2024; (14(3)) doi:10.3390/diagnostics14030248.

    PMID: 38337764
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    Hot Phases Cardiomyopathy: Pathophysiology, Diagnostic Challenges, and Emerging Therapies.

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    Current cardiology reports 2025; (27(1)):11.

    PMID: 39786662
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    Arrhythmogenic Right Ventricular Cardiomyopathy Presenting as Clinical Myocarditis in Women.

    Scheel PJ, Murray B, Tichnell C, et al.

    The American journal of cardiology 2021; (145()):128-134 doi:10.1016/j.amjcard.2020.12.090.

    PMID: 33460606
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    Myocarditis-like Episodes in Patients with Arrhythmogenic Cardiomyopathy: A Systematic Review on the So-Called Hot-Phase of the Disease.

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    Biomolecules 2022; (12(9)) doi:10.3390/biom12091324.

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    Myocardial inflammation detected by cardiac MRI in Arrhythmogenic right ventricular cardiomyopathy: A paediatric case series.

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    PMID: 29885824
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    Diagnosis of Arrhythmogenic Cardiomyopathy in a Young Patient With Recurrent Myocarditis: The Importance of Genetic Testing.

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    The American journal of cardiology 2025; (242()):37-40 doi:10.1016/j.amjcard.2025.01.034.

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    A Systematic Analysis of the Clinical Outcome Associated with Multiple Reclassified Desmosomal Gene Variants in Arrhythmogenic Right Ventricular Cardiomyopathy Patients.

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    Electrical dysfunctions in human-induced pluripotent stem cell-derived cardiomyocytes from a patient with an arrhythmogenic right ventricular cardiomyopathy.

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    Arrhythmogenic response to isoproterenol testing vs. exercise testing in arrhythmogenic right ventricular cardiomyopathy patients.

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This page explains the symptoms and warning signs of Arrhythmogenic Cardiomyopathy (ACM) for educational purposes only. Always consult your cardiologist or seek emergency care if you experience fainting, unexplained chest pain, or rapid heartbeats.

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