ABSTRACT: Cardiac output (CO) in 12 infants of diabetic mothers (I DMs) and in 20 normal neonates (control group) was estimated evaluating blood velocity in ascending aorta, using a gated pulsed Doppler velocimeter with a 5MHz transducer positionated in the suprasternal nocth. CO (mL/min/Kg) was calculated from the equation: CO = SV · HR, where SV-stroke volume (mL/Kg) and HR = heart rate (bpm). Ventricular septal hypertrophy (IVDS>0.35 cm) was found in 5 of 12 IDMs, but in none control group. In the group with IVDS > 0.35 cm, CO and SV were reduced at comparable HR. Reduced CO in IDMs with hypertrophic cardiomyopathy was related to lower SV, due to decreased left ventricular compliance and limited pre-load.