Despite its clinical use as a sensitive measure of left ventricular performance, little is known about whether the Tei index is influenced by aging. We determined the Tei index in 141 subjects without cardiovascular disease (age 16-78 years). There were statistically significant variations in ejection time, isovolumic relaxation time, and the Tei index with aging. There was a moderate linear correlation between isovolumic relaxation time and age (r = 0.49, P <.001) and the Tei index and age (r = 0.33, P <.001). This investigation demonstrated that when assessing myocardial performance in patients using this index, age-normalized values should be used.