dyspnea
Dyspnea is the uncomfortable feeling of not getting enough air — what most people simply call shortness of breath. It is a subjective sensation, an experience reported by the patient, much like pain or hunger. A small amount after running hard is normal; the medical concern is breathlessness that is out of proportion to the effort, or that appears at rest.
Many systems can produce dyspnea, but in cardiology the common mechanism is congestion: when the left side of the heart cannot pump forcefully enough, blood backs up into the lungs and fluid leaks into the air spaces. Stiff, wet lungs are harder to inflate and worse at taking up oxygen, so breathing feels like a struggle. Lung disease, anemia, deconditioning, and anxiety can cause the same sensation, so the cause must be reasoned out rather than assumed.
Clinicians grade how much exertion triggers it — from breathlessness only on strenuous effort to breathlessness at rest — using scales such as the NYHA classification for heart failure. Patterns matter too: cardiac dyspnea often worsens when lying flat and may wake a person at night, clues that distinguish it from many lung causes.
A man who once climbed two flights of stairs easily now must stop and catch his breath halfway up — a worsening of exertional dyspnea that prompts evaluation for heart failure.
A falling exercise tolerance is a practical way to track worsening cardiac dyspnea.
Dyspnea is one of the most common reasons people seek cardiology care, but it is not specific to the heart — distinguishing cardiac from pulmonary causes often relies on a blood test such as BNP plus a chest image and echocardiogram.