It is widely assumed that heartbeat dynamics are chaotic, although the
re has been no evidence confirming such an opinion, and some evidence
to the contrary. Additionally, the deterministic assumptions of such d
ynamics cannot be demonstrated. An alternative model is presented base
d upon the notion of terminal dynamics, which can more faithfully repr
esent key features of the heartbeat: namely, piecewise determinism, an
d singular points between beats, which allow for adaptability while ma
intaining stability.