Models of cardiac electrodynamics are useful tools in understanding electrical activities in heart. Currently, whole heart models often used a continuum approach, where the heart is treated as a syncytium. Models which incorporate the detailed cellular structure, have only been applied for sections of cardiac tissue. To date, no whole vertebrate heart models incorporating cellular details such as gap junctions have been developed, because of the computational power required. Therefore how detailed cellular arrangements and intercellular connectivity affect cardiac conduction at a whole heart level remains unclear. This thesis described such cell based models of larval zebrafish hearts. The model scales range from one cell, to cardiac tissue and then to the whole heart which were modelled with finite element modelling software. These models are able to reproduce published electrophysiological results including, the electrocardiogram, action potentials and conduction velocities in different regions. By varying in intercellular electrical connectivity, a cardiac condition: atrioventricular block was simulated which is comparable to experimental results qualitatively. As the models are able to estimate the gap junction resistances, they can be used in investigating the role of gap junctions in cardiac propagation. These models can be improved by adding more histological details in the future.