S1 and S2 are the normal heart sounds you hear when the heart valves close. Heart murmurs are extra sounds that can be heard during systole, diastole, or as a continuous sound. S3 and S4 are abnormal ...

Doctors can fail to identify obvious heart murmurs because they've listened to normal and murmur heart sounds too little. But slapping the contrasting sounds onto mp3 players helps train docs quickly.