Sternal displacement during CPR was measured in 11 adults and 2 manikins (Recording Resusci Anne) while the chest was compressed with variable maximum pulse compression force at a rate of 60/min with compression duration of 0.5-0.6 sec. In 10 patients, the pulsatile sternal elastic characteristic can be satisfactorily described with a 2nd degree polynomial F = beta Ds + gamma D2s, where beta = 54.9 +/- 29.4 (mean +/- SD) N/cm is the pulsatile initial elasticity and gamma = 10.8 +/- 4.1 N/cm2 is the posterior resiliency. The sternal characteristics of manikins were linear F = kDs with high elasticity constants, k = 131 and 142 N/cm. Therefore, the manikins tested differ significantly in elasticity characteristics from the human chest during resuscitation. In general, the manikin: (1) has markedly greater stiffness at the onset of compression, and (2) maintains a linear stiffness throughout the usual range of displacement, rather than becoming stiffer with greater chest displacement.