Cor pulmonale is the enlargement and failure of the right ventricle of the heart in response to lung disease or other causes of increased pulmonary pressure. It has a chronic progressive course but can also worsen acutely with life-threatening complications. Key factors in cor pulmonale include pulmonary hypertension from conditions like COPD, pulmonary embolism, or vascular disease, leading to right ventricular hypertrophy and eventually right-sided heart failure if left untreated. Prognosis depends on underlying cause and can be improved with treatments like oxygen therapy and smoking cessation.