“As a rule, the smaller the heart in proportion to the body, the more efficient it is; an enlarged heart usually means softened muscles. [Paavo Johannes] Nurmi [1897-1973], the Finnish runner, owes his great endurance, physicians say, to the fact that his heart is only about half the normal size and beats only fifty times a minute. A slow-beating heart generally lasts longer than one which pulsates rapidly; and in general, the muscular condition or ‘tone’ of the whole body is reflected in the heart’s structure. Soft muscles mean a soft heart, which is why violent exercise often causes the death of those unused to exertion.”