Just 6 decades ago, the introduction of right heart catheterization provided investigators their very first opportunity to explore the previously inaccessible pulmonary circulation. This marked the dawn of the new era of pulmonary vascular physiology. Just measuring the pulmonary arterial pressure for the first time was noteworthy. Virtually nothing was known about the regulation of the pulmonary blood vessels. Interestingly, one of the very first investigations was to measure the effect of acute hypoxia in man.1 A rise in pulmonary arterial pressure was noted, but this was erroneously ascribed to a passive response of increasing pulmonary blood flow. Shortly, a follow-up publication acknowledged the overestimation of cardiac output, and when this was corrected, the increase in pressure was attributed to pulmonary vasoconstriction. This was the physiological response to acute hypoxia, but obviously, the effects of long-term chronic hypoxia were completely unknown.