The main symptom is extreme tiredness. Not enough blood is pumped from the heart to the muscles. The body diverts blood away from less vital organs and muscles to focus on supplying the heart and brain.
Heart failure may affect the left, right or both sides of the heart. If the left half of the heart is weak, fluid will build up in the lungs due to congestion of the lungs' veins. If the right half of the heart is weak, general body and vein pressure will increase, and fluid will accumulate in the body, especially tissues in the leg and stomach areas.
The oxygen and nutrients in the blood provide the body with the energy it needs to operate efficiently. Heart failure causes breathlessness and fatigue because of the heart cannot function as it should.