Peripheral vasodilatation determines cardiac output in exercising humans: insight from atrial pacing

Key points •  During exercise, cardiac output is regulated to match oxygen delivery to the metabolic demand. •  This study evaluated the role of heart rate and peripheral vasodilation in the regulation of cardiac output during exercise. •  We increased heart rate by atrial pacing in 10 healthy male individuals during three different conditions: at rest, during exercise and during femoral arterial ATP infusion at rest. •  Increasing the heart rate by atrial pacing by up to 54 beats min −1 did not increase cardiac output in any of the three given conditions as there was a proportional decrease in stroke volume. •  These results indicate that cardiac output is regulated by changes in peripheral vasodilatation, whereas an increase in heart rate is less important.