Cardiac sympathetic nerve activity (CSNA in imp/s) was measured in the postganglionic fibers of awake cats at rest, during body movement, and with excitement. The CSNA showed synchronized discharges with various periodicities. Rhythms of the synchronized CSNA were analyzed by an interval histogram (IIH). The IIH showed a multimodal distribution. The first model interval (Tc) was in a range of 75 to 125 ms. An 8-12 cycle/s Tc rhythm, i.e., inverse value of Tc, was always observed in the awake cat at rest and during body movements. Probability of the 8-12 cycle/s Tc rhythm was smallest at rest, increased during body movement, and was largest with excitement. These results suggested that the 8-12 cycle/s Tc rhythm, observed in all states in the conscious cat, is a fundamental rhythm of central cardiovasomotor origin. The subsequent model distribution (Tb = 2 x Tc, 3 x Tc, 4 x Tc, or 5 x Tc) ranged from 150 to 700 ms, mostly 200 to 500 ms. A 2-5 cycle/s Tb rhythm, i.e., inverse value of Tb, appeared more frequently at rest than that during body movement or with excitement. A new model concerning a mechanism to cause the 2-5 cycle/s Tb rhythm is suggested.