The lungs are the primary organs of respiration in humans and many other animals. Humans have two lungs, a right lung and a left lung. They are situated within the thoracic cavity of the chest. The right lung is bigger than the left lung, as the left lung shares space in the chest with the heart. The lungs together weigh approximately 1.3 kilograms (2.9 lb), with the right lung weighing more than the left.