For the first time unstable periodic orbits(UPO's)are extracted from experimental human ECG signals for the quantitative classification of normal and abnormal cases. The normal cardiac system is characterized by three or four UPO's whereas pathological conditions such as premature ventricular contraction (PVC), Ventricular Fibrillation(VF), and Atrioventricular(AV) block shows different trends in the number and distribution of the UPO's.