264 DURATION OF CARDIAC PHASES. [BOOK i. 



which is held. And on the view that the ventricles still remain 

 contracted for a brief period after the valves are shut, the second 

 sound does not mark the end of the systole, and the duration of 

 the systole is rather longer than the time given above. 



Accepting the view given in the text, we may make the 

 following statement. In a heart beating 72 times a minute, 

 which may be taken as the normal rate, each entire cardiac cycle 

 would last about 0*8 sec., and taking 0'3 sec. as the duration of 

 the ventricular systole, the deduction of this would leave 0'5 sec. 

 for the whole diastole of the ventricle including its relaxation, the 

 latter occupying less than '1 sec. At the end of the diastole of 

 the ventricle there occurs the systole of the auricle, the exact 

 duration of which it is difficult to determine, it being hard to say 

 when it really begins, but which, if the contraction of the great 

 veins be included, may perhaps be taken as lasting on an average 

 O'l sec. The 'passive interval' therefore, during which neither 

 auricle nor ventricle is undergoing contraction, lasts about '4 sec. 

 and the absolute pause or rest during which neither auricle nor 

 ventricle is contracting or relaxing about *3 sec. The systole 

 of the ventricle follows so immediately upon that of the auricle, 

 that practically no interval exists between the two events. In 

 the systole of the ventricle we may distinguish the phase during 

 which pressure is being got up before the semilunar valves are 

 opened ; this is exceedingly short, probably from '02 to '03 sec. 

 During the rest of the '3 sec. of the systole, the contents of the 

 ventricle are being pressed into the aorta. 



The duration of the several phases may for convenience' sake 

 be arranged in a tabular form as follows : 



sees. sees. 



Systole of ventricle before the open- 

 ing of the semilunar valves, while 

 pressure is still getting up '03 



Continued contraction of the ventricle, 

 and 



Escape of blood into aorta '27 



Total systole of the ventricle '3 



Diastole of both auricle and ventricle, \ 

 neither contracting, or " passive in- 

 terval " *4 I 



Systole of auricle (about or less than) f l j 



Diastole of ventricle, including relaxa- 

 tion and filling, up to the beginning 

 of the ventricular systole '5 



Total Cardiac Cycle " '8 



