Many biological variables, including electrophysiological processes in the heart, scale with body mass. Cardiac electrophysiological parameters have been scaled only for mammals. Because avian and mammalian hearts differ in several structural and functional facets, the purpose of this study was to estimate how the duration of ventricular excitation scales with body mass, heart rate, and heart mass in birds. Values of the QRS complex duration, body mass, and heart rate for non-passerine species representing 13 families and 10 orders were obtained from published data, covering three orders of magnitude in body mass. The findings of the study were as follows: the QRS complex duration scaled with body mass to the power of 0.18, with heart rate to the power of −0.45, and with heart mass to a power close to 0.195. The duration of ventricular excitation in birds is related not only to morphologic (body mass, heart mass) but also hemodynamic (heart rate) parameters by the power law. Further investigations of scaling relations between QRS and cardio- and hemodynamic parameters is useful to find out an evolutionary importance and causes of peculiarities of cardiac electrophysiology in birds and some mammalian species.
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