Failure of the right side of the heart caused by prolonged high blood pressure in the pulmonary artery and right ventricle of the heart. Normally, the left side of the heart produces a higher level of blood pressure in order to pump blood to the body; the right side pumps blood through the lungs under much lower pressure. Any condition that leads to prolonged high blood pressure in the arteries or veins of the lungs (called pulmonary hypertension) will be poorly tolerated by the right ventricle of the heart. When this right ventricle fails or is unable to properly pump against these abnormally high pressures, this is called cor pulmonale.