Your doctor will help you decide if you need a CRT-D device, but here are some criteria. If you have a ventricular dysynchrony, which means the two lower heart chambers don't beat in synch. If your medications are at the maximum dosage, but do not adequately treat your symptoms. If your heart failure has been classified by your doctor as Class III or IV. If your ejection fraction-that's the percentage of blood pumped out of your heart with each beat-is 35% or below. Or if your heart's electrical activity (as measured through "QRS duration") is prolonged.