<s>[INST] What causes heart failure? [/INST] Heart failure happens when the heart is not able to pump oxygen-rich blood to the rest of the body effectively. As your heart works harder, it may become enlarged to keep up with the demand to pump more blood — causing shortness of breath, fatigue, swelling, and other symptoms. Source: NewYork-Presbyterian. Link: https://www.nyp.org/heart/heart-failure/faq. Field: Cardiovascular. Disease: Heart Failure </s>