(2009) Cardiovascular Dysfunction with Low Cardiac Output Due to a Small Heart in Patients with Chronic Fatigue Syndrome, Miwa et al

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https://www.jstage.jst.go.jp/article/internalmedicine/48/21/48_21_1849/_article - free PDF at https://www.jstage.jst.go.jp/article/internalmedicine/48/21/48_21_1849/_pdf/-char/en

A paper from 2009, made somewhat newly topical by people being worried about covid-19 cardiac symptoms in the non-acute phase.

Raising fun questions on if these are covid symptoms, or CFS ones.
Or, indeed, if people with specific preexisting heart morphologies that are normally benign are more prone to CFS.

Results Slender build (body mass index <20 kg/m2) was common (47%). Possible cardiovascular symptoms including shortness of breath (32%), dyspnea on effort (28%), rapid heartbeat (38%), chest pain (43%), fainting (43%), orthostatic dizziness (45%) and coldness of feet (42%), were all frequent complaints. Hypotension (28%) was occasionally noted. Electrocardiograms frequently revealed right axis deviation (21%) and severe sinus arrhythmia (34%) suggesting accentuated parasympathetic nervous activity. Small heart shadow (cardiothoracic ratio ≤42%) was noted on the chest roentgenogram in 32 patients (60%). Echocardiographic examination demonstrated low cardiac indexes (<2 L/min/m2) with low stroke volume indexes (<30 mL/m2) due to a small left ventricular chamber in 19 (36%, p<0.05 vs. 8% in 36 controls). None had reduced left ventricular ejection fraction.

72% of the patients report PEM as a symptom, so it is at least somewhat reasonable caseness-wise.