Which of the following instruments is used to listen to the heartbeat? 

A stethoscope is an instrument that can be used to detect the heartbeat. The sounds generated by the heart's contractions and relaxations can be easily heard through the use of a stethoscope. The sound that the heart makes is caused by these contractions and relaxations. These "lub" and "dub" noises are caused by the tricuspid valve and semilunar valve shutting.