HI, It is my understanding that a baby with a heart condition, depending on the type and severity, must have monitered for specific amounts because if they take in too much fluid it can stress the heart and cause problems. This is what we have been told here. As far as the pre-post weighs, they would be a great option, except that if the baby is onnly to have, say, 1.5 oz per feed then you have to keep weighing the baby during the feed to make sure you don't go over. Jay Simpson, CLE Sacramento, CA "No Miracles performed here, just a lot of love and hard work." LACTNET Quilt Raffle Check out the web page then e-mail me at [log in to unmask] for where to send for your tickets!