On the Aesir Heart

The heart of an adult Aesir is structurally adapted, and not merely enlarged in proportion to his size, to a body whose mass, blood volume, and metabolic demand would impose severe strain on an ordinary cardiovascular system. Aesir cardiac muscle is thick, highly vascularised, and remarkably efficient. Their resting pulse is generally slower than that of Humans, yet stroke volume is enormous. Blood pressure varies less dramatically under exertion than one might expect, and oxygen delivery remains stable even during sustained heavy labour.

This is not without cost. The Aesir heart tolerates chronic workload extremely well but responds poorly to certain forms of rhythm disturbance. Several arrhythmias that are merely concerning in Humans can become catastrophic in Aesir because so much circulation depends upon maintaining strong, coordinated contractions. It is therefore quite possible for an Aesir to spend eight hours hauling timber, lifting loads which would injure three Humans, and walking beside a mammoth through freezing rain, only to be rendered gravely ill by a disturbance of rhythm subtle enough that a Human might initially describe it as “palpitations.” Nature is fond of such bargains.