A dual head stethoscope allows you to listen to both high and low frequency sounds. The bell is used for low frequencies while the diaphragm is used for higher frequencies. This allows listening to a wider range of sounds than would be available from a traditional single headed stethoscope like the Littman Lightweight II.
It will pick up not just sounds from the heart and lungs but also from the carotid arteries and abdomen.
You can buy this double headed stethoscope in two form – “Econo” and “Nova”. The Nova has a sensitive aluminium chestpiece that provides clearer acoustics and superior fidelity at higher frequencies.