Additional Study Information: This prospective, multicenter trial is looking at the investigative device called the ACURATE Transcatheter Aortic Valve System for TAVR to see if it is safe and effective in treating patients with severe symptomatic native aortic stenosis. The ACURATE Transcatheter Aortic Valve System for TAVR is designed for iliofemoral access and delivery of a self-expanding implant that restores competency in a sclerotic aortic valve. To implant the device, a surgical incision is made in the femoral vein (incision in the upper leg between the knee and the hip). A catheter is advanced into the heart access the aortic valve. The TAVR delivery system is inserted into the heart. The doctor uses echocardiography (imaging of the heart using sound waves) and fluoroscopy (moving X-rays) to visualize placement of the device. As the TAVR implant is slowly released from the delivery system, it expands back up to its normal size and the doctor positions the implant within the aortic valve. After placement of the TAVR implant, the delivery system is pulled out of the heart through the femoral vein and the incision in the leg is closed. Patients are randomized to receive either the ACURATE valve or a commercially available valve. Patients will be expected to return for follow-up visits at 1 month, 6 months, and every year through 10 years (years 6, 8, & 9 are telephone visits.)