Pediatric and adolescent patients who are receiving cardiac resynchronization therapy with biventricular pacing as a method of treating chronic heart failure. Children of both genders, who are followed in the Division of Pediatric Cardiology at Primary Children's Medical Center, who meet all inclusion and no exclusion criteria are eligible for participation in this clinical study.

No intervention is administered as part of this study. Prospective longitudinal case series study to describe and evaluate clinical and hemodynamic effects of CRT and to identify echocardiographic predictors of positive response to CRT in Group described.

The purpose of this study is to collect information on patients with chronic heart failure who have already been identified by their physician as candidates for CRT. All tests, including device implantation are standard of care for patients undergoing CRT. The only test involved in this study that is not standard of care is the quality of life questionnaire. Patients who undergo CRT system implant will be followed post-implant (up to 1 week), and at one month, three months, six months and twelve months. The only test involved in this study that is not standard of care is the quality of life questionnaire.

Composed of 23 items comprising 4 dimensions. 5-point Likert scale from: 0 (Never) to 4 (Almost always).

Higher scores = Better health related quality of life (HRQOL)

Composed of 23 items comprising 4 dimensions. 5-point Likert scale from: 0 (Never) to 4 (Almost always).

Higher scores = Better health related quality of life (HRQOL)

Describe the relationship between echocardiographic measures and subject response to CRT