Heart failure means that the heart isn't pumping as well as it should be. Your body depends on the heart's pumping action to deliver oxygen- and nutrient-rich blood to the body's cells. When the cells are nourished properly, the body can function normally. With heart failure, the weakened heart can't supply the cells with enough blood. This results in fatigue and shortness of breath. Everyday activities such as walking, climbing stairs, or carrying groceries can become very difficult.