  Identity verification is an increasingly important process in our daily
lives, and biometric recognition is a natural solution to the authentication
problem.
  One of the most important research directions in the field of biometrics is
the characterization of novel biometric traits that can be used in conjunction
with other traits, to limit their shortcomings or to enhance their performance.
  The aim of this work is to introduce the reader to the usage of heart sounds
for biometric recognition, describing the strengths and the weaknesses of this
novel trait and analyzing in detail the methods developed so far by different
research groups and their performance.
