In a monitor for monitoring diastolic relaxation of a ventricle of a
heart, an impedance signal is measured in a ventricle of the heart and
the occurrence of a notch in the impedance signal coincident with the
entry of blood into the monitored ventricle is detected by forming a time
derivative of the impedance signal and generating a loop by plotting
impedance values of the impedance signals with respect to related time
derivative values to form a loop for each cardiac cycle of the heart, and
comparing the generated loop to a loop template representing a normal
loop for the subject, to identify deviations in the loop from normal
deviations in timing and shape of the notch.