Mathematical models have been remarkably effective in the study of diastolic ventricular mechanics. However, significant pitfalls are found in the misapplication of models and concepts, especially when proper attention is not paid to all the variables that affect the range of their applicability. Models incorporate two ideas: the measurement of variables and parameters, and their interrelationships. With regard to measurement, due attention is not always paid to the frequency response characteristics required in signal acquisition and processing. This results in waveform distortions and spurious time delays. These should be avoided or appropriate corrections made. The inattention to the range of applicability of various concepts and models in the literature represents a source of misleading conclusions and controversy. This is demonstrated by means of several examples. © 1988.