Letters to the Editor Last Word: Point:Counterpoint author responds to commen-

taries on “Active venoconstriction is/is not important in main-taining or raising end-diastolic volume and stroke volume during exercise and orthostasis” To the Editor: Hainsworth and Drinkhill (1) and I (4) agree that active venoconstriction is real and that more research is needed to define its role in humans. I suggest, however, that the sympathetic activity data from humans with acute myocardial infarction (1, 1a) cannot be extrapolated to that for normal humans. Magder (2) states that cardiac output increases in proportion to oxygen consumption and increased heart rate in accord with the relative workload. I agree with these facts. However, to conclude that cardiac output and heart rate are thus “con-trolled ” variables is not valid. The cardiovascular is a closed loop system in which volume redistribution (via the principl