Patterns and mechanisms involved in the onset and development of cardiac function in a number of crustacean groups are critically reviewed. Irrespective of phylogeny, heart design and ecology, the onset of heart beat seems inextricably linked to the ontogeny of the thoracic segments where the heart is located. Initially the beat is erratic but soon becomes regular and the rate increases as development proceeds. However, still early in development the relationship between heart rate and body size shifts from a positive to a negative one. Nevertheless cardiac output continues to increase with increasing development, via increasing stroke volume. Some species in more ‘primitive’ groups develop and retain a myogenic heart beat. Others, with globular and tubular hearts, exhibit a shift from myogenicity to neurogenicity around the time the body size vs. heart rate relationship becomes negative. Very early cardiac function seems generally insensitive to external factors, such as temperature, oxygen and pollutants. Sensitivity to environmental factors increases with development, perhaps over the same timescale as the cardiac regulatory mechanisms appear.