BACKGROUND The purpose of this study was to determine whether oral midazolam 1.5 mg x kg(-1) is a safe and effective alternative to standard-dose midazolam (0.5-1.0 mg x kg(-1)) premedication for infants and children with congenital heart disease. METHODS A total of 193 infants and children (4 months to 2 years) undergoing cardiovascular surgery were studied. Each patient received 0.5, 1.0, or 1.5 mg x kg(-1) of oral midazolam. The level of sedation was assessed with a 5-point scale and vital signs were measured including blood pressure (BP), heart rate (HR) and oxyhaemoglobin saturation (SpO2) before and after the medication. RESULTS Infants and children premedicated with oral midazolam 1.5 mg x kg(-1) were better sedated than those with standard-dose midazolam: 4% of infants and children given 1.5 mg x kg(-1) of midazolam became agitated compared with 14% given 1.0 mg x kg(-1) and 26% in those given 0.5 mg x kg(-1). Ninety percentage of infants and children given 1.5 mg x kg(-1) of midazolam achieved satisfactory sedation (calm, drowsy, or asleep) in 30 min, whereas 68% in those given 1.0 mg x kg(-1) and 35% in those given 0.5 mg x kg(-1). Midazolam 1.5 mg x kg(-1) did not cause any statistically significant decrease in BP, HR, or SpO2, although eight infants and children showed > or =20% drop in systolic BP and six infants and children showed >5% drop in SpO2. No 'spelling attacks', seizure-like activity, apnoea, nor laryngospasm were observed in any infants and children during and after the medication. CONCLUSIONS Oral midazolam 1.5 mg x kg(-1) is excellent for preanaesthetic medication for infants and children undergoing cardiovascular surgery.