My Baby Girl Is 15 Days Old. When She Was

My baby girl is 15 days old. when she was in womb her heart ..... all are fine. In 8th month ultra sound gave mild iugr.In 9th month also same. Due to low weight we went for C section(they tried labour but after having tablet bay herat beat is at 170. So went for C-section).At delivery time baby weight is 2.2 kg.Now (15 days old) her weight is 2.6 K.g. Every thing is fine but doctor asked us for 2d echo right now. He said heart beat is not normal. What i do?