The purpose of this study is to collect and compare information on how and when adolescent
heart transplant recipients take their prescribed medication. The investigators want to find
out if regular use of 'an app' on cell phones, called the Teen Pocket PATH® (TPP), can help
adolescents take their medication according to their prescribed dosing schedule. This may
then help reduce complications of transplant, such as rejection. The investigators also want
to find out if how adolescent heart transplant recipients take their medications affects the
development of antibodies in their blood. Antibodies are small proteins in the blood that may
develop after heart transplantation, and which can sometimes damage a new heart.