BACKGROUND: Infants with moderate to severe congenital heart disease (CHD) are at a higher risk for growth failure and malnutrition due to increased metabolic demands and inadequate energy intake. This state requires meals that are more frequent and a special enriched diet, which may have negative implications on oral health. AIM: To examine the oral colonisation of some bacteria associated with caries development during infancy; mutans streptococci (MS) and lactobacilli (LCB) in infants with CHD and whether their dietary intake had an impact on the bacterial levels. DESIGN: This was a prospective case-control study. 11 infants with CHD and 22 healthy, age-matched infants were enrolled. Saliva samples and food diaries were collected at 6, 9, and 12 months of age. The total viable counts of MS and LCB in saliva were determined, and energy intake, meal frequency, intake of proteins, fat, carbohydrates and sucrose were calculated. RESULTS: At 12 months of age, the MS count was higher in the CHD group than in the controls (p Key words: Congenital heart disease, diet, meal frequency, mutans streptococci.