NATURE 255 
THURSDAY, JANUARY 6, 1870 
THE LABOURING FORCE OF THE 
HUMAN HEART 
“Pea is no organ in our bodies that has a more 
important influence upon health, at all ages of our 
lives, than the heart, whose rhythm and force are governed 
by laws of nerve-force, of which we are at present almost 
totally ignorant. Regarded, however, from a mechanical 
point of view, as a hydraulic pumping machine, our know- 
ledge of the heart is more accurate, and may yet lead the 
way to greater knowledge of the physiological action of 
this vital organ. 
I propose, in the present communication, to give an 
estimate of the daily labouring force of the human heart, 
and to compare it with that of other muscles, such as 
those used in rowing or climbing, reserving for a future 
communication the proof of the data to be now employed. 
The heart, regarded as a pumping machine, consists of 
two muscular bags (veztricles), one of which drives the 
blood through the lungs, and the other through the entire 
body. This blood is forced, by a pumping action, repeated 
seventy-five times each minute, through both lungs and 
body, and experiences in each case a resistance which is 
measured by the hydrostatical pressure of the blood in 
the pulmonary artery and aorta. The resistance offered 
to the circulation of the blood, by the capillary vessels of 
the lungs and body, is different ; but the total quantity of 
blood that passes through the lungs and body in a given 
time, must be the same ; from which it follows, that the 
resistance offered by the capillaries must be in the pro- 
portion of the hydrostatical pressure in the great arteries 
leading from the ventricles of the heart. If, therefore 
we knew that pressure for one side of the heart, and the 
relative forces of the two ventricles in contracting, we 
should know the entire resistance overcome by the heart 
at each of its beats. 
If, in addition to the hydrostatical pressure in one 
ventricle, and its ratio to that in the other ventricle, 
we knew also the quantity of blood forced out of each 
ventricle against this pressure, we should have all the 
elements necessary to calculate the labouring force of the 
heart, as will be presently shown. 
I demand, therefore, that my reader shall grant me, 
provisionally, the following postulates, which are neces- 
sarily three in number :— 
I. That three ounces of blood are driven from each 
ventricle at each stroke of the heart. 
IJ. That the hydrostatical pressure in the left ventricle 
and aorta, against which the blood is forced out, amounts 
to a column of blood 9923 feet in vertical height. 
IlI. That the muscular force of the left ventricle, in 
contracting, bears to that of the right ventricle the pro- 
portion of 13 to 5. 
With these postulates granted, we may now proceed to 
calculate the daily labouring force of the heart as follows. 
At every stroke of the heart,three ounces of blood are forced 
out of the left ventricle against a pressure of a column of 
blood 9°923 feet in height. The work done, therefore, at each 
stroke is equivalent to lifting three ounces through 9°923 
feet. This work is repeated 75 times in each minute, 
and there are 60 X 24 minutes in the day. Hence, the 
ON 
daily work of the left ventricle of the human heart is 
3 X 9'923 X 75 XK 60 X 24 ounces lifted through one foot ; 
or, since there are 16 ounces in the pound, and 2,240lbs. 
in the ton, the work done by the left ventricle of the heart 
3 X 91923 X 75 X 60 X 24 
16 X 2,240 
one foot. Multiplying and dividing out this quantity, we 
find the daily work of the left ventricle is 89°706 foot-tons. 
The work done by the right ventricle is five-thirteenths of 
this quantity (post. III.) ; the daily work of the right ven- 
tricle is therefore 34°502 foot-tons. Adding these two 
quantities together, we find for the total daily work of the 
human heart 124°208 tons lifted through one foot. 
It is not easy for persons unaccustomed to these cal- 
culations to appreciate quickly the enormous amount of 
labouring force denoted by the preceding result; but in 
order to. facilitate this appreciation, I shall compare it 
with the following descriptions of labour :— 
1. The daily labour of a working man. 
2. The work done by an oarsman in an eight-oar boat- 
race. 
3. The work done by locomotive engines, or animals 
climbing a height. 
1. The daily labour of a working man, deduced from 
various kinds of labour, from observations spread over 
many months, is found to be equivalent to 354 tons lifted 
through one foot, during the ten hours that usually con- 
stitute the day’s work. This amount of work is less than 
three times the work done by a single heart, beating day 
and night for 24 hours: thus, three old women sitting 
beside the fire, alternately spinning and sleeping, do more 
work, by the constant beating of their hearts, than can 
be done in a day by the youngest and strongest “ navvy.” 
2. If an Oxford eight-oar boat be propelled through 
the water at the rate of one knot in seven minutes, the 
resistance offered by the water may be estimated at 
81°36 lbs. by calculation, or at 74°15 lbs. by actual obser- 
vation. From this result, and from the fact that 575 
ounces of muscle are employed by each of the eight 
oarsmen, we can calculate that 15 foot-pounds of work 
are expended by each ounce of muscle during each 
minute of work. 
No labour that we can undertake is regarded as more 
severe than that of the muscles employed during a boat- 
race; and yet this labour, severe as it is, is only three- 
fourths of that exerted day and night during life by each 
of our hearts. 
The average weight of the human heart, which increases 
with age (for obvious reasons), may be estimated from 
the following tables :— 
tons lifted through 
in one day is 
Average oz. 
1. Meckel . 10'0 
2, Cruveilhier . 75 
3. Bouilland 8-4 
2h dbe)osivety 5 5 4 5 95 
5. Boyd (at. 30—40) 10°4 
6. Boyd (zt. 40—50) 10°5 
Mean é TORSO) 
From this weight, and the work done by the heart in 
one day (124 foot-tons), we can calculate the work done 
by each ounce of the heart in one minute, as follows :— 
Work done by the human heart, in foot-pounds per 
124208 X 2240 
ounce per minute, = 
9°39 X 24 X 60 
= 20°570 foot-pounds, 
