Assessment of the isolated right atrium as a pump

The ability of the hemodynamically isolated dog right atrium to pump against a resistance equivalent to normal pulmonary artery pressure was tested in an in vivo preparation. At a preload of 10 mm. Hg, the right atrium reached a peak systolic pressure of 18.2 mm. Hg (±1.3 S.E.M.) against an afterload of 12 mm. Hg, but it could eject a flow only equivalent to 53 percent (±6) of the dog's cardiac output (n = 6). At a preload of 15 mm. Hg, a peak systolic pressure of 21.5 mm. Hg (±0.8) was recorded against an afterload of 17 mm. Hg, but again, only 55 percent (±5) of the dog's cardiac output was ejected. It appears that the cardiac output from the nonhypertrophied right atrium is limited by the strength of the right atrial contraction and the physiological limits imposed by the venous driving pressure.