On-X Heart Valve - 17mm Aortic and 23mm Mitral

Inclusion Criteria: 1. Patients of any age; unless waived by local IRB assent of the patient and in all cases consent of parent or legally authorized representative is required if a patient is under the age of majority and not legally emancipated. 2. Patients who are sufficiently ill to warrant replacement of their diseased natural or prosthetic valve, based on standard cardiovascular diagnostic workups. 3. Patients who are in sufficient satisfactory condition, based on the physical exam and investigator's experience, to be an average or better operative risk, (i.e., likely to survive one year postoperatively). 4. Patients who require an isolated aortic valve replacement size 17 mm or isolated mitral valve replacement size 23mm. 5. Patients who are geographically stable and willing to return to the implanting center for follow-up visits. 6. Patients or legally authorized representatives who are adequately informed of their participation in the clinical study and what will be required of them in order to comply with the protocol. 7. Patients requiring concomitant cardiovascular surgery, such as coronary bypass may be included in the study. Exclusion Criteria: 1\. Patients who are pregnant, planning to become pregnant or are lactating. 2 Patients who have a noncardiac progressive disease, which in the investigator's experience produces an unacceptable increased risk to the patient. 3 Patients who have a documented history of substance (drug or alcohol) abuse or are prison inmates. 4\. Patients with a previous prosthetic valve, where it is not being replaced by a study valve, or patients requiring multiple valve replacement. 5\. Patients with active endocarditis or active myocarditis. 6 Patients who require tricuspid or pulmonic valve replacement. 7. Patients who have not agreed to return for the required number of follow-up visits or who are geographically unavailable for follow-up. 8\. Patients who cannot be maintained on long-term anticoagulant therapy. 9. Patients with non-cardiac illness resulting in a life expectancy of less than 1-year. 10\. Patients previously enrolled and implanted in this trial may not re-enter after withdrawal. 11\. Patients already enrolled in another investigational device or drug study (nor can enrolled patients be enrolled in other studies). 12\. Patients with acute preoperative neurological deficit, myocardial infarction, or cardiac event who have not returned to baseline for at least 30-days prior to enrollment. 13\. Patients with aortic aneurysm or other medical condition that creates a higher than usual risk of surgical complication. 14\. Patients who are prisoners or mentally ill, and pediatric patients who are incapable of understanding their assent as judged by the principal investigator.