Under public concert conditions, the heart rate of a musical performer increases significantly when compared with that in a rehearsal situation. Previous studies have examined this effect, attributing a higher heart rate in performances to the effects of mental stress and performance anxiety. However, the actual physical work load had to be neglected in these studies, because it appears to be impossible to quantify physiological involvement while playing music. The present study investigates the basic physiological and psychological processes that take place during a performance by investigating the heart activity of performers during performance, rest and listening phases, and correlating the acquired data to synchronous acoustic recordings. The study also shows that the occurrence of special cardiac events such as VES and SVES generally correlate with musically demanding moments.