FIG. 1.

Biological models differ in applicability and sophistication. Biological models for the human body exist on a continuum of physiological applicability and model sophistication. Animal models are more sophisticated as they spare a human subject and are applicable in that they demonstrate the systemic effect of a treatment. Isolated cells, organ-on-a-chip, and 3D human cell models are more sophisticated approaches that allow for continuous observation and greater control over the stimuli provided to the heart cells but are incapable of recreating the influence of tissue-level and total systemic responses. Human heart organoids recreate tissue-level responses, and the idealized goal of a total organ system model would be capable of realizing total systemic responses. 2D, two-dimensional; 3D, three-dimensional. Color images are available online.