Chaos theory was received with the great enthusiasm. It has provided a new, attractive approach to irregular, nonperiodic phenomena: apparently stochastic behaviour might be explained by a few nonlinear differential equations. During the last years, it became clear that chaos in the exact sense is hardly to be proved in real systems, such as the cardiac dynamics. Despite this fact, new methods, originally developed for chaotic signals, are successfully applied to fetal ECG extraction, noise filtering and heart dynamics modelling.

        Key words: fractal, chaos, cardiology, models of heart dynamics