irritable heart

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orthostatic intolerance

A condition (OMIM:604715) characterised by lightheadedness, fatigue, altered mentation, syncope and tachycardia upon assuming an upright position, and markedly elevated serum norepinephrine. 

Molecular pathology
Defects in SLC6A2, which encodes a member of the sodium:neurotransmitter symporter that regulates norepinephrine homeostasis, are a cause of orthostatic intolerance.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

irritable heart

An obsolete term for neurocirculatory asthenia or effort syndrome, characterized by breathlessness, palpitation, weakness, and exhaustion.
See also: heart
Medical Dictionary, © 2009 Farlex and Partners