The principal findings of this study were the following: (1) HRR1 was significantly lower in IPAH than that in normal subjects; (2) CRI was detected in 89.7% IPAH patients (n = 52), 53% with HRR < 16 beats; (3) a decrease in the heart rate recovery after exercise was associated with worse NYHA functional class, impaired chronotropic response, increased NT-proBNP, and decreased exercise capacity. This evidence concerns the gene NPPB and idiopathic pulmonary arterial hypertension.