Exceptions
The most obvious exception/disrepancy to the Billion Heartbeats 'rule' is of course the Human Being. Humans reach one billion heart beats by about thirty years of age but thanks to medicine, a good diet and technology, we manage to live much longer. The average Western life span would cover 2.5-3 billion heart beats. However, note that the life-span is markedly lower in undeveloped, poverty stricken parts of the world.
As a little side note, the science-fiction film "Logan's Run" was set in a future where Humans were discarded/culled at the age of 30...more than a coincidence maybe?
Domestic animals (i.e Pets, Farm animals, Zoo animals) can also be exceptions to the general rule. This may well be due to factors such as selective breeding and better general health-care, vaccination/protection from disease, improved nutrition and living conditions.
Crtics may point out anomolies and certain species in which the quarter-power scaling laws do not seem to hold, but the history of physics is replete with cases where an elegant model came up against some recalcitrant data, and the model eventually won.
The content on this site has been drawn from a wide range of Web & printed resources and edited/summarised to form a single point of reference and overview of the Billion Heart Beats.