OBJECTIVES: An increase with age in pulmonary arterial pressure (PAP) during exercise has been shown, but the extent to which this limits exercise capacity in older people remains unclear. One possibility is that exercise-induced hypoxic pulmonary vasoconstriction (HPV) can limit exercise capacity. It is known that intravenous iron blunts HPV. The aim of this study was to examine the hypothesis that intravenous iron abrogates increased PAP during exercise in older individuals. Furthermore, we assessed whether this would have an impact on maximal exercise capacity. METHODS: Thirty-two volunteers aged between 50 and 80 years with no or mild cardiovascular or respiratory diseases were studied in a double-blind, block-randomized, placebo-controlled protocol with 5 follow-ups. Sixteen volunteers received a 50-ml intravenous iron injection (15 mg/kg; maximum dose: 1 g) as ferric carboxymaltose. The other 16 volunteers were given a 50-ml saline injection as placebo. Systolic pulmonary artery pressure (SPAP), stroke volume (SV) and cardiac output (CO) and were assessed during rest and light exercise (a rise in heart rate of 30 bpm) by Doppler echocardiography. Maximal exercise capacity was determined by peak oxygen consumption (VO2peak) and peak work rate on a cycle ergometer. Heart rate (HR) and oxyhaemoglobin saturation (SpO2) were also measured during exercise. Haemoglobin (Hgb), erythropoietin (EPO), serum iron, ferritin, soluble transferrin receptor (sTfR) concentrations were tracked from blood samples. All volunteers completed the exercise assessments and gave blood samples before the injection, and at 4 hours, 23 hours, 7 days, 4 weeks and 8 weeks. RESULTS: A difference in serum iron concentration between groups was present after the injection and persisted for 7 days. Ferritin and sTfR concentrations rose and decreased respectively in the iron group at 23 hours after the injection and these changes persisted for the following 8 weeks. A fall in EPO concentration following iron injection was observed at 23 hours and 7 days. In contrast, Hgb concentration did not show a difference between groups throughout the study. Linear mixed-effects modelling demonstrated that prior iron infusion attenuated the rise in SPAP in response to exercise for a period of at least 8 weeks, the end point of the study (p = 0.002). There were no significant differences between groups demonstrated in SV and CO throughout the follow-ups. VO2peak and peak work rate, as well as HR and SpO2 at the peak exercise level, showed no differences between groups in the study. CONCLUSIONS: Our findings demonstrate that SPAP during exercise in elderly people is reduced by iron infusion. However, decreasing SPAP during exercise by intravenous iron injection does not affect exercise capacity in this group.