Miwa, Kunihisa, Fujita, Masatoshi · Clinical cardiology · 2011 · DOI
This study found that ME/CFS patients who experience dizziness or fainting when standing up (orthostatic intolerance) have smaller hearts and pump less blood with each beat compared to ME/CFS patients without these symptoms and healthy people. The researchers used ultrasound imaging to measure heart size and function in different groups and discovered that about half of ME/CFS patients with orthostatic intolerance had unusually small left heart chambers.
This study identifies a potential cardiac mechanism for orthostatic intolerance, a debilitating symptom affecting many ME/CFS patients. Understanding that a subset of ME/CFS patients have measurably smaller hearts and reduced cardiac output could lead to targeted diagnostic approaches and interventions tailored to this physiological abnormality.
This study demonstrates association but does not prove causality—it is unclear whether small heart size causes ME/CFS and orthostatic intolerance, or whether they result from a common underlying process. The cross-sectional design cannot establish whether cardiac changes precede symptom onset. Additionally, the study does not determine why some ME/CFS patients develop small hearts while others do not.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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Primary citation
Miwa, Kunihisa & Fujita, Masatoshi (2011). Small heart with low cardiac output for orthostatic intolerance in patients with chronic fatigue syndrome.. Clinical cardiology. https://doi.org/10.1002/clc.20962
BibTeX
@article{mecfsatlas-miwa-2011-small-heart,
author = {Miwa, Kunihisa and Fujita, Masatoshi},
title = {Small heart with low cardiac output for orthostatic intolerance in patients with chronic fatigue syndrome.},
journal = {Clinical cardiology},
year = {2011},
doi = {10.1002/clc.20962},
note = {PubMed: 22120591},
url = {https://www.mecfsatlas.com/evidence/miwa-2011-small-heart},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-27. https://www.mecfsatlas.com/evidence/miwa-2011-small-heart
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