Pulmonary hypertension describes raised pulmonary circulatory pressure, venous or arterial. Venous pulmonary hypertension is more common in daily practice than primary arterial hypertension. The rise in pulmonary venous and arterial pressure represents pressure overload for the right ventricle. With the right ventricular myocardial thickness being thin, it responds to the pressure afterload by giving way and stretching, hence the enlargement of the right ventricular and right atrial cavities. Severe cases of raised right ventricular pressure will eventually affect left ventricular function through the ventricular interaction mechanism.