Extension to QTI571A2301 to Evaluate the Long-term Safety, Tolerability and Efficacy of Imatinib in Severe Pulmonary Arterial Hypertension (PAH)

Inclusion Criteria: * Patients who participated in CQTI571A2301 clinical trial and completed the week 24 visit of the study protocol, including all Study Completion assessments * Patients who withdrew from the CQTI571A2301 study prematurely for reasons not related to study drug or not related to a safety issue but performed all Study Completion assessments Exclusion Criteria: * Patients with a pulmonary capillary wedge pressure \> 15 mmHg at time of Study Completion assessments in core protocol CQTI571A2301. If pulmonary capillary wedge pressure is not attainable, then a left atrial pressure measurement may be used in its place. * LVEF \< 45% * Patients with thrombocytopenia, platelet count \< 50E9/L (50E3/µL) * Patients with uncontrolled systemic arterial hypertension, systolic \> 160 mmHg or diastolic \> 90 mmHg * Patients with a QTcF \> 450 ms for males and \> 470 ms for females in the absence of right branch bundle block (based on Visit 1 ECG if required to be performed) Other protocol-defined inclusion/exclusion criteria may apply