Entrainment between heart rate and weak noninvasive forcing

We demonstrate that the heart rate of a healthy human can be synchronized b y means of weak external noninvasive forcing in the form of a sequence of s ound and light pulses, being either periodic or aperiodic, the latter forci ng given by interbeat intervals of the heart of another subject. The phenom enon of phase locking of n : m type is observed for both situations in abou t 90% of our experiments. The plot for the ratio of forcing frequency to th e average frequency of response versus detuning possesses a plateau and is in agreement with classical synchronization theory.