The heart undergoes a contraction cycle that begins once the ejection from the previous cycle is complete, necessitating the relaxation of the heart. As the heart relaxes, the mitral valve opens to allow blood to flow from the atrium to the ventricle, preparing for the next heartbeat.

In patients with severe mitral stenosis, a significant reduction in the return volume of blood to the heart occurs. This reduction diminishes the pumping action of the ventricle, leading to disuse atrophy of the left ventricle. Normally, the left ventricle is relatively large and capable of maintaining a normal heart shape.

When the left ventricle atrophies, it results in the heart having a flatter, more rounded apex, leading to a pear-shaped heart. If the ventricles are unable to efficiently reclaim blood, the load on the left atrium increases. Consequently, the left atrium enlarges, appearing larger at the top and smaller at the bottom in an X-ray, resembling a pear. This is how a pear-shaped heart is formed.