Normal Heart Sounds 



dactyl into eight parts (though, for the scheme of the sounds and 

 the pause, four would have served equally well), the eight divisions 

 are now needed for the demonstration of the workings of the auricles 

 and ventricles ; thus : 



I s - sound \a n -sound\ .pause \ 



Ventricles Ventricles 



contracting dilating 



Thus, the auricles are filling during seven-eighths of the dactyl, and 

 are emptying their contents into the ventricles in the eighth part, and, 

 immediately after this emptying, the ventricles, which are now full to 

 the utmost, contract, and the auricles begin to fill again. As regards 

 the ventricles, they are contracting during the first four parts of the 

 dactyl and dilating during the remainder. 



The first sound takes place with contraction of the ventricles and 

 is synchronous with the arterial pulse. It is due chiefly to the slam- 

 ming of the auriculo-ventricular valves, and partly, perhaps, to the rush 

 of blood out of the ventricles ; to the impulse of the apex against the 

 chest-wall, and to the rumble of the contracting ventricular walls. 

 With the first sound, then, the auriculo-ventricular gateways are shut, 

 and the aortic and pulmonary are open. 



The short second sound is due to the sharp closure of the semilunar 

 valves, which takes place when the ventricles have finished their con- 

 traction, and the elastic coats of the pulmonary artery and aorta are try- 

 ing to drive the blood back into the flaccid ventricles. It is like the 

 noise which is caused by the vibration in a long, vertical, leaden pipe 

 when the tap, through which water is quickly flowing, is suddenly 

 turned off. 



Take the hem of your handkerchief between the finger and thumb 

 of your left hand, and about 3 in. along in the straight line take it also 

 between the finger and thumb of the right hand. Now, by suddenly 

 separating the two hands after having slightly approximated them, 

 jerk the hem tight, and you get a long vibration or sound, some- 

 thing like that due to the sudden tension of the flaps of the auriculo- 

 ventricular valves. That represents the long first sound. Now, in a 

 similar way, snap the hem with the thumbs about an inch apart, and 

 you will imitate the short, ringing, second sound. 



The fuller the large arteries, and the greater the pressure of the 

 blood down upon the semilunar valves, the louder, sharper, and more 



