Several different microphones have been designed throughout the years to accomplish very different tasks. Some mics--such as condenser microphones--pick up a great deal of sound from several directions, while others pick up one focused sound only from one direction. Of this latter group, the cardioid microphone is perhaps the most popular, as it picks up almost exclusively the desired sound while ambient noise is hardly noticeable.

The cardioid microphone is so named because of its pattern of sensitivity, which is roughly shaped like a heart when drawn out on an axis. This means most of the sound a cardioid microphone picks up comes from the front of the mic, while minimal noise is picked up from the rear and only marginal noise is picked up from the sides. This type of sensitivity pattern makes the cardioid microphone useful in myriad situations, including but not limited to situations in which several mics are being used at one time, live performances, and certain recording purposes.

A cardioid microphone may be a condenser microphone--which uses a capacitor system to pick up sound--or a dynamic microphone, which utilizes a coil attached to a diaphragm. When the diaphragm vibrates, it in turn moves the coil, which then creates electromagnetic induction.

As a unidirectional microphone--that is, a mic that picks up sound from only one direction--the cardioid microphone is designed to pick up one sound well, with other ambient noises fading into the background. If the cardioid microphone still isn't enough to eliminate ambient noise for a user's purposes, the supercardioid microphone eliminates even more noise from directly behind the microphone. The supercardioid mic is often confused with the hypercardioid microphone, which actually does not eliminate as much noise behind the mic, but eliminates more to the sides. Out of the three types of cardioid microphone mentioned, the hypercardioid is considered the most directional.

For musical purposes, a cardioid microphone is particularly useful for live sound, such as concerts. It can also be used as a vocal mic for presentations, public address, and other situations that require a vocal mic. The cardioid microphone is also a good choice for recording concentrated sounds such as vocals and certain types of drums.

Other situations in which a cardioid microphone may be used include household applications, such as in a telephone. The microphone in the handset picks up primarily the speaker's voice while eliminating other ambient noise, such as background conversation or television chatter.