In 1963, an expert committee of the World Health Organization defined cor-pulmonale as “hypertrophy of the right ventricle resulting from diseases affecting the function and/or structure of the lungs...,”but this pathological definition is in fact of limited value in clinical practice. Mild-to-moderate pulmonary hypertension is a common complication of chronic obstructive pulmonary disease (COPD); such a complication is associated with increased risks of exacerbation and decreased survival. Habitual lung conditions as well as conditions of the pulmonary vessels beget increased pulmonary vascular resistance. The most common beginning medium causing increased pulmonary blood pressure (pulmonary hypertension) is by pulmonary vasoconstriction, activation of coagulation pathway and annihilation of pulmonary arterial vessels. Pulmonary hypertension causes pressure load on the right ventricle and hence right ventricular blowup. Originally, there's right ventricular hypertrophy, but as cardiac decompensation sets in and right heart failure ensues, dilatation of right ventricle occurs. In patients with COPD, clinical signs may be masked by lung hyperinflation. Most patients initially have dyspnea, which becomes more severe as right ventricular failure occurs. Chest pain may occur and be difficult to differentiate from angina pectoris. In patients with severe COPD, orthopnea, worsening right ventricular function, bloating and early satiety occurs. The goal of treatment is to control symptoms. It is important to treat medical problems that cause pulmonary hypertension, because they can lead to Cor- pulmonale. As per NICE (National Institute for Health and Care Excellence) guidelines, the treatment of Cor pulmonale is Long Term Oxygen Therapy. Key words: Cor-pulmonale, Pulmonary hypertension, COPD, Oxygen, pulmonary arterial pressure