Pulmonary hypertension and related diseases, like pulmonary arterial hypertension, can be treated by administering an effective dose of a CDK inhibitor, including palbociclib, 6-acetyl-8-cyclopentyl-5-methyl-2-{[5-(piperazin-1-yl)pyridin-2yl]amino}pyrido[2,3-d]pyrimidin-7(8H)-one, or pharmaceutically acceptable salt thereof.
