Although pulmonary arterial hypertension originates in the lung and is caused by progressive remodeling of the small pulmonary arterioles, patients die from the consequences of pressure-overload-induced right heart failure. Prognosis is poor, and currently there are no selective treatments targeting the failing right ventricle. Therefore, it is of utmost importance to obtain more insights into the mechanisms of right ventricular adaptation and the transition toward right heart failure. In this review, we propose that the same adaptive mechanisms, which initially preserve right ventricular systolic function and maintain cardiac output, eventually initiate the transition toward right heart failure.