Background: Pulmonary arterial hypertension (PAH) is a chronic debilitating illness. The effects of vigorous aerobic exercise training (AET) on heart function in PAH are poorly understood. Methods: 18 women with PAH (age 56.2 ± 8.8 yr, BMI 28.8 ± 7.3 kg/m 2) underwent 10 wk of vigorous AET. Cardiac function was observed at rest and peak exercise using bioelectrical impedance cardiography before and after the AET. Cardiac function was observed in a small PAH subset (n = 7) for 10 wk prior to beginning the AET. A cohort of sedentary women (n = 19) served as healthy controls. Results: Left ventricular ejection fraction (EF; 48 ± 9.2 vs. 61.5 ± 13.3 %, P = .034) and the systemic vascular resistance index (SVRI; 2258 ± 419.1 vs 2939 ± 962.4 dyn•s/cm 5 •m 2 , P = .008) were lower at supine rest in the baseline PAH group vs healthy group, as were peak exercise heart rate (HR; 140 ± 13.3 vs 170 ± 13.8 beats/min, P < .001) and SVRI (828 ± 141.1 vs 824 ± 300.9 dyn•s/cm 5 •m 2 , P = .050) after controlling for age and HR. SVRI measured at peak exercise decreased in the PAH group after AET (828 ± 141.1 vs 766 ± 139.6 dyn•s/cm 5 •m 2 , P = .020). Early diastolic left ventricular filling ratio (EDFR) worsened in the PAH subset prior to AET (95.9 ± 19.4 vs 76.2 ± 18.9%, P = .043) and remained unchanged after AET. Conclusion: Vigorous AET was not associated with significant declines in left ventricular systolic or diastolic function in women with PAH. AET may be beneficial for reducing afterload and may preserve left ventricular diastolic function.