I Had Open Heart Surgery In May To Repair My

I had open heart surgery in May to repair my mitral valve. In the last few weeks I have noticed a feeling of something moving in the centre of my chest just under my rib cage. It reminds me of how it felt to have my baby moving or kicking in the womb. I sometimes feels like a fluttery feeling. My doctor says it might be cartilage and she's not worried about it and I shouldn't be either. She says it can take up to a year for things to settle down after open heart surgery. Do you know what might be happening and if i need to seek medical attention?