Since peds cardiac ICU pays my bills, I might be able to help. You've heard correctly that the acuity is high and the patients are generally neonates or infants. Most cardiac defects are corrected early in life; older children may need internal pacemakers, valve repairs or replacements or dilatation of vessels. Some repairs in older patients (those approaching adulthood) may need revision. But most of the patients will be little. The American Association of Critical-Care Nurses Core Curriculum for Pediatric Critical Care Nursing (2nd Edition)is a fabulous resource, as is Nursing Care of the Critically-Ill Child (3rd Edition) by Mary Fran Hazinski. Amazon has a good selection of reference books for Kindle, which could be a good alternative to a pocket manual.
Review fetal circulation. This has an impact on pretty much every cardiac patient in one way or another. For children with cyanotic defects, it's desirable to maintain their fetal circulation until they can get to the OR.
Review the anatomy of the most common defects: hypoplastic left heart, pulmonary atresia, transposition of the great arteries, tetralogy of Fallot, coarctation of the aorta, atrial septal defect, ventricular septal defect and atrioventricular septal defect. This will help you understand the underlying circulatory impairment and what might be a consideration post-operatively. Think about how mechanical ventilation (positive pressure) and oxygen therapy may affect the different defects and what might have to be adjusted for optimal treatment. Even if you don't totally get it, asking intelligent questions will make you look like a rock star!
Review the commonly-used drugs: alprostadil, nitroglycerin, epinephrine, norepinephrine, milrinone, amiodarone, nitroprusside, captopril, furosemide, ethacrynic acid, sildenafil, nitric oxide (inhaled), epoprostinol, sotalol, digoxin and carvedilol. Have a general knowledge of what they do and when they're used. Don't expect to know them inside and out though. You should also think about analgesia and sedation - they're vital to successful critical care.
I hope you enjoy your consolidation and that you get the job in the end of it all!