doxo is a secure all-in-one service to organize all your provider accounts in a single app, enabling reliable payment delivery to thousands of billers. doxo is not an affiliate of Children's - Sibley Heart Center Cardiology. Logos and other trademarks within this site are the property of their respective owners. No endorsement has been given nor is implied. Payments are free with a Linked Bank Account. Other payments may have a fee, which will be clearly displayed before checkout. Learn about doxo and how we protect users' payments.