This talk provides an overview of two projects I undertook during my PhD in applied mathematics and the following year as postdoc at the Queensland University of Technology, Brisbane (Australia). The first project deals with differential operators of non-integer order that have been used with success in a variety of practical applications to describe transport processes in media characterised by spatial connectivity properties and high structural heterogeneity altering the classical laws of diffusion. The second one introduces the population of models approach, a method often used to build a set of parameters able to capture and describe the variability observed in experimental data. In both cases, particular reference will be made to mathematical models of cardiac electrophysiology.