Swedish researchers monitored different singers’ heartbeats while doing a variety of vocal tasks such as reading parts of text, humming, singing a song and singing a 10 s mantra phrase. The result of the group study was a revealed connection between the length of the phrases sung and HRV (Heart Rate Variability) frequencies. When the members who took part in the study sang together in unison their pulses synchronized.
In other words their hearts beat as one when they were singing together.
According to the study, the researchers believe that the synchronization of the heart beat is due to breath coordination during singing. The singers’ pulses sped up and slowed down at the same rate. When inhaling the pulse goes up, when exhaling the pulse goes down.