Much effort has been made to determine the parameters of signal propagation and signal generation in excitable tissues like cardiac muscle, nervous tissues and smooth muscle. For a single nerve fibre the electrical situation is relatively easy to describe and mathematical and biophysical descriptions are possible. In smooth muscle or cardiac muscle surrounding cells may be also coupled to the signal source and a mathematical description or physiological analysis has too many variables to give a clear picture of the propagation. Moreover, when cells are dissolved from the tissue, the membrane properties might be determined by patch clamp analysis; the coupling between the cells remains unclear. When the tissue contains more than one cell type (pacemaker cell, muscle cell, epithelial cells) the situation will become even more complex and the description will remain with many variables.

This problem can be solved with a three dimensional network analysis which demonstrates the coupling parameters under in vitro conditions.

Spontaneously rhythmical active tissue was loaded with an excitation-sensitive dye (calcium, membrane potential). Using fast confocal microscopy, excitation was measured during time intervals of at least 3–5 activity periods. Using three dimensional cross-correlation procedures, the similarity of a signal in the distance delta x, delta y from a fixed x,y position was determined. A piezo stepper serves for measuring the Z-axis. Cross correlation gives as an additional measure the time lag between the two signals and velocity of the signals. Using this approach, signal propagation under normal and stimulated conditions can be determined in a complex tissue. Moreover, pacemakers and signal sources can be identified.