A single dose of sildenafil improves exercise capacity in Fontan patients. However, a recent study failed to show a long-term effect of sildenafil. This study evaluated whether there are factors that might predict sildenafil effects.

We studied 36 patients (16–42 years, 14 female) with univentricular heart after various modifications of the Fontan surgery (13 APC, 16 AVC, 7 TCPC). They performed two cardiopulmonary exercise tests, with at least 120 min rest and a single dose of 50 mg sildenafil in between.

After sildenafil administration, patients improved their peak oxygen uptake from 64.5 to 67.3 % predicted (p = 0.0003) without change in ventilatory efficiency (\({\dot{\text{V}}}_{\text{E}} /{\dot{\text{V}}\text{CO}}_{2}\) slope), oxygen saturation (SpO₂) at rest or at peak exercise, respiratory exchange ratio. In addition, resting systolic blood pressure was slightly reduced after sildenafil administration. There was a moderate negative correlation of this improvement to baseline peak oxygen uptake (r = −0.395; p = 0.017). The change in peak oxygen uptake could not be correlated to time of surgery, type of surgery, NT-pro-BNP, or to other clinical data. Nevertheless, all four patients with NT-pro-BNP levels higher than 1,000 pg/ml had the most prominent improvements in exercise capacity.

Fontan patients have an improved exercise capacity after a single dose of sildenafil. Patients with worse baseline peak oxygen uptake profit more.