Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a medically unexplained illness characterized by severe fatigue limiting normal daily activities for at least 6 months accompanied by problems with unrefreshing sleep, exacerbation of symptoms following physical or mental efforts (postexertional malaise [PEM]), and either cognitive reports or physiological evidence of orthostatic intolerance in the form of either orthostatic tachycardia and/or hypocapnia. Although rarely considered to have cardiac dysfunction, ME/CFS patients frequently have reduced stroke volume with a significant inverse relation between cardiac output and PEM severity. Magnetic resonance imaging of ME/CFS patients compared with normal control subjects found significantly reduced stroke, end-systolic, and end-diastolic volumes together with reduced end-diastolic wall mass. Another cardiovascular abnormality is reduced nocturnal blood pressure assessed by 24-hour monitoring. Autonomic dysfunction is also frequently observed with postural orthostatic tachycardia and/or hypocapnia. Two consecutive cardiopulmonary stress tests may provide metabolic data substantiating PEM.

肌痛性脑脊髓炎/慢性疲劳综合征 (ME/CFS) 是一种医学上无法解释的疾病，其特征是严重的疲劳限制了正常的日常活动至少 6 个月，并伴有睡眠不足、身体或精神努力后症状加重（劳力后不适 [PEM]） )，以及直立性心动过速和/或低碳酸血症形式的直立不耐受的认知报告或生理证据。虽然很少被认为有心功能不全，但 ME/CFS 患者的每搏输出量经常减少，心输出量与 PEM 严重程度呈显着负相关。与正常对照受试者相比，ME/CFS 患者的磁共振成像发现中风、收缩末期、和舒张末期容积以及舒张末期壁质量减少。另一种心血管异常是通过 24 小时监测评估的夜间血压降低。自主神经功能障碍也经常在体位性直立性心动过速和/或低碳酸血症中观察到。两次连续的心肺压力测试可以提供证实 PEM 的代谢数据。