Stress hyperglycemia, a state of abnormal metabolism with supra-normal blood glucose levels, is often seen in critically ill patients. Tight glycemic control (TGC) was originally shown to reduce morbidity and mortality in a landmark randomized clinical trial (RCT) of adult critically ill surgical patients but has since come under intense scrutiny due to conflicting results in recent adult trials. One pediatric RCT has been published to date that demonstrated survival benefit but was complicated by an unacceptably high rate of severe hypoglycemia. The Heart And Lung Failure - Pediatric INsulin Titration (HALF-PINT) trial is a multi-center, randomized clinical treatment trial comparing two ranges of glucose control in hyperglycemic critically ill children with heart and/or lung failure. Both target ranges of glucose control fall within the range of "usual care" for critically ill children managed in pediatric intensive care units. The purpose of the study is to determine the comparative effectiveness of tight glycemic control to a target range of 80-110 mg/dL (TGC-1, 4.4-6.1 mmol/L) vs. a target range of 150-180 mg/dL (TGC-2, 8.3-10.0 mmol/L) on hospital mortality and intensive care unit (ICU) length of stay (LOS) in hyperglycemic critically ill children with cardiovascular and/or respiratory failure. This will be accomplished using an explicit insulin titration algorithm and continuous glucose monitoring to safely achieve these glucose targets. Both groups will receive identical standardized intravenous glucose at an age-appropriate rate in order to provide basal calories and mitigate hypoglycemia. Insulin infusions will be titrated with an explicit algorithm combined with continuous glucose monitoring using a protocol that has been safely implemented in 490 critically ill infants and children.