Usually, but not necessarily. Perhaps you were retaining fluid around the heart, and Lasix was needed. Or perhaps you have another medical condition which is treated by Lasix. You should discuss this with your cardiologist. What you need to find out is how well the heart is pumping, and they need to check the ejection fraction of the left ventricle.
Diuretics remove water from the person's body.
Their benefit is that they making people feel better by removing water which otherwise would collect in the lungs and legs. This helps people breath better and can decrease leg pain and discomfort. I heard that selenium could help or prevent heart failure. There is no clear research on selenium in heart failure, and generally we do not recommend any vitamin supplement because we simply don't know if they will hurt or help someone. These drugs help dissolve the clot that forms during a heart attack which helps the blood get to the heart muscle sooner than without.