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

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.

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