For 29 patients with congestive heart failure (CHF), 24-hour noninvasive ambulatory blood pressure (ABP) and heart rate (HR) measurement profiles were described, using the periodogram method, and were compared with the same findings in 22 matched controls. Right-sided heart catheterization was performed in all patients. The mean cardiac index was 2.2 L/min/m2 (range 1.3 to 2.9 L/min/m2). More severe CHF, as assessed by cardiac index, pulmonary artery wedge pressure, and right atrial pressure, correlated significantly with a reduction in the amplitude of the circadian ABP and HR rhythms (0.38 less than r less than 0.63; p less than 0.05). Moreover, a reduced increase in cardiac index during cycloergometric exercise in 11 CHF patients correlated with a blunting of the circadian systolic ABP and HR profiles (0.57 less than r less than 0.90; p less than 0.05). Our results indicate that there is a reduction in the amplitude of the circadian BP and HR rhythms related to the severity of CHF.