Dictionary.net

Soldier's heart, D.A.H., neurocirculatory asthenia, a cardiac neurosis due to over strain, marked by rapid pulse, dyspnea, and various neurotic symptoms, associated with an increased susceptibility to fatigue, observed especially in soldiers in active war service but noted occasionally also in civil life.

Disordered action of the heart (D.A.H.), a syndrome of nervous and cardiocirculatory disturbances associated with an increased susceptibility to fatigue, observed especially in soldiers on active war service (fighting or marching), but noted occasionally also in civil life.

A functional disorder of the heart from muscular exhaustion. It is especially common among soldiers; and with them may be attributed to forced marches, fever, and camp diarrhea.