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Average levels of central venous pressure (CVP) and cardiac output (CO) during steady-state exercise (solid symbols) and peak muscle metaboreflex activation (crossed symbols); under intrinsic heart rate (HR) and contractility responses (circles), constant HR by rapid ventricular pacing (triangles), and constant HR in association with limited contractility by pacing plus β1-blockade (squares); in control (white symbols) and heart failure (black symbols), N = 5.
