Sudden momentary fluctuations of left ventricular, aortic, right ventricular, and pulmonary arterial pressure were noted during isovolumic relaxation of the respective ventricles. The presence of such transients raised questions related to their meaning and significance. The purpose of this report is to emphasize the nonartifactural nature of these pressure transients and to describe their origin and significance in the cardiac cycle. Pressure transients were observed in 31 of 32 patients with normal aortic valves, and in 17 patients with normal pulmonary valves in whom right-sided measurements were made. Such transients, however, were absent on the left ventricular and aortic pressure recordings of three patients with calcific aortic stenosis. These sudden changes in pressure are indicative of momentary compressions and rarefactions of the blood that occur within the ventricles and their respective arterial chambers. Whenever present, pressure transients were noted to occur coincident with the major aortic or pulmonary components of the second sound. Since intraaterial sound pressure is derived from the pressure signal by litering the low frequencies and amplifying the high frequencies, one can deduce that intraarterial sound pressure is in fact a representation of these pressure changes. The recognition of these pressure transients on an otherwise smooth ventricular, aortic, or pulmonary arterial pressure places in proper perspective their role in the production of the second heart sound.