Suggest Treatment For Septal Defect And Stent On Legs

I m a 61 year old male and have been told after a echo that I have a septal defect. I don t understand how it was not detected before. I ve had several cath procedures to place stents in legs. I ve had a complete dye study done from lower legs to brains and all in between. Any cliues as to why this would not have been seen before