It may seem paradoxical that the American Civil War and World War I, both of which witnessed slaughter on a previously unimaginable scale, should provoke such intense interest in soldiers' hearts. Yet, during and between these wars there was much discussion of a condition which incapacitated many thousands of otherwise healthy troops. This condition, characterised by chest pains, palpitations, breathlessness, fatigue, syncope and exercise intolerance, became known during 1860s as the irritable heart of soldiers. By the First World War the terminology had changed to soldier's heart, then to neurocirculatory asthenia. In this study, the author brings to bear his expertise as a historian, professor of medicine and a former soldier to analyse the condition and to trace the changing medical and social attitudes to it. By viewing the condition through the dual lenses of history and modern medical knowledge, this work provides a unique perspective on one of the pioneering areas of Anglo-American cardiology.