The study of diastolic function, in particular, the creative application of noninvasive modalities, such as echocardiography and MR imaging, requires an understanding and appreciation of the basic physiology of left ventricular filling dynamics. The physics and physiology of diastolic function and dysfunction is examined by relating the phasic patterns of transmitral flow to the properties of the cardiac chambers. Particular attention is paid to the equations governing the transmitral pressure-flow relations and the active and passive chamber properties that determine the flow patterns: Active relaxation, passive compliance, viscoelasticity, and elastic deformation. The physiologic role of diastolic suction is discussed within this context.