CRD Summary: This review concluded that sildenafil produced significant improvement in functional and clinical parameters of pulmonary hypertension compared to placebo, but showed no differences compared to bosentan. This review was carried out robustly, but the small number of primary trials make the results difficult to interpret. The authors' conclusions reflect the evidence presented, but appear strong given the limited data available.

CRD Commentary: This review addressed a clear question supported by appropriate inclusion criteria. Relevant databases were searched, although it was unclear whether language restrictions were applied. Efforts were made to retrieve unpublished data. Suitable methods were used throughout the review process to minimise the risks of reviewer error and bias. Although validity was assessed, the table describing the details of assessment was missing a key, which would no doubt add significant value.

Heterogeneity was reported in the forest plots, but was not discussed. Significant heterogeneity for the main outcomes may mean the the decision to pool studies in meta-analyses was not appropriate.

In terms of methodology, this review was carried out robustly, but the small number of primary trials and small trial sizes make the results difficult to interpret. The authors' conclusions are based on the evidence presented, but appear a little strong given the limited data available for evaluation.