To evaluate the impact of Pulmonary Arterial Hypertension (PAH) therapies on the incidence of pericardial effusion and its prognostic implications for patient survival. Methods: This retrospective cohort study included 60 patients diagnosed with PAH at a high-volume tertiary care center, treated with intravenous or subcutaneous prostanoids. Data were collected from 2015 to 2019, including echocardiographic assessments, right heart catheterization, World Health Organization functional class evaluations, six-minute walk distance tests, and biomarkers such as brain natriuretic peptide and N-terminal prohormone of brain natriuretic peptide. Follow-up was conducted at least 90 days post-treatment initiation. Results: Pericardial effusion was observed in 31.7% of patients before therapy. Patients with moderate to large effusions had a significantly higher mortality risk (HR = 1.92; 95% CI 1.1–44.78; p = 0.0044), while small effusions appeared protective (HR = 0.27; 95% CI 0.15–0.48; p = 0.006). Survival rates declined from 89% at one year to 71% at three years post-therapy, with effusion presence correlating with more severe PAH manifestations. Conclusions: Initial pericardial effusion severity is a critical predictor of mortality in PAH patients. Early assessment and stratified management of pericardial effusion are essential for optimizing therapeutic outcomes in PAH management. Future research should explore targeted interventions for managing pericardial effusion to improve patient prognosis.