Cardiac responses to exercise (eg, increased heart rate and contractility) depend on sympathetic stimulation. An assessment of circulatory responses to exercise in subjects with diminished sympathetic activity, then, should provide clues as to the role played by central factors in these hemodynamic responses. In this case, if peripheral factors are primary, systemic venous return should increase normally, and, since heart rate would not rise appropriately, left ventricular filling and LVED would increase. This would result in an exaggerated rise of stroke volume, causing a normal rise in Q according to the Starling principle. On the other hand, if central cardiac factors are primary, heart rate and contractility responses would be dampened (with a diminished rise in Q), with a fall in atrial pressures, stroke volume, and ventricular diastolic dimension.