Is the normal heart rate chaotic?

In its June 2008 issue, the editors of [_Chaos_](http://chaos.aip.org/)
announced a new feature, "Controversial Topics in Nonlinear Dynamics". The
first controversial topic to be aired is "Is the Normal Heart Rate Chaotic?".
Since major impediments to achieving consensus on the statistical properties
of biologic time series have included the lack of open access time series,
PhysioNet has provided a set of 15 heart beat (RR-interval) time series in
health and disease (congestive heart failure and atrial fibrillation). Each
time series is about 24 hours long (roughly 100,000 intervals), and is
provided as a text file for analysis and as an image for visual review. All of
the time series were derived from continuous ambulatory (Holter)
electrocardiograms. We encourage participants in the Chaos Controversies issue
to use the 15 RR interval time series provided here as a common focus of
analysis.