To my mind, there are no homeopathic specifics for any problem as (presumably) serious as this. In your place I would want to know what exactly the cardiac (or other) abnormality was, the birth history, the child's family history, and the mother's physical, emotional and mental state during the pregnancy, as well as any salient homeopathically useful characteristics of the baby itself. My other thought is that given that cardiologists don't often want to put pacemakers in babies (well not around here, anyway), I would consider most carefully whether to treat this condition homeopathically at all.