We describe our experience with 2 patients having Costello syndrome, aged 11 and 36 months, who suffered systolic anterior motion of the aortic leaflet of the mitral valve and obstructive cardiac hypertrophy requiring surgery, comparing their cardiac characteristics to those described previously. We conclude that the heterogeneous nature of the cardiac hypertrophy in this syndrome can be considered and managed as the sum of a diffuse hypertrophy accessible to beta-blockade, and an asymmetric hypertrophy accessible to surgical myomectomy.