The brainstem makes its decisions regarding the rate and depth of breathing on the basis of information it receives from the body. The information includes the level of oxygen in the air, the level of oxygen in the blood, the level of expired gas, carbon dioxide, in the blood and the acidity or alkalinity of the blood. The carbon dioxide level is the single most critical factor for controlling the rate and depth of breathing. This is because the carbon dioxide level reflects the rate of energy consumption. Shortness of breath in heart disease Shortness of breath, difficulty breathing, a conscious awareness of breathing, can occur because of disease of one or more of heart valves.
Shortness of breath can occur because of heart muscle failure.
This is called a cardiomyopathy. The heart is a muscle, a pump, that circulates fluid through the body. If the heart muscle is damaged by repeated heart attacks, or by inflammation, or by drugs such as alcohol, the pump fails and fluid, edema, accumulates in the lungs. This is called peri-carditis. Shortness of breath can occur because of an altered heart rhythm.