Left ventricular ejection fraction is known to be unchanged or slightly increased with advancing age. This echocardiographic study, including 40 healthy subjects 18 to 70 years old, shows that this is a net effect of decreased contractions in the long axis and increased in the short axis. From age 18 to 70 years, the longitudinal shortening decreases by 20% (P < .001) and the short-axis diameter shortening increases by 18% (P=.012). Multiple regression analysis showed strong correlation to age for both short- and long-axis contractions and no significant additional explicatory power when the variables systolic blood pressure, left ventricular wall thickness, heart rate, or sex were included. There was no significant correlation between diameter changes during the isovolumic phases and age. The findings have practical implications when calculating ejection fraction from M-mode measurements. Teichholz's formula will overestimate ejection fraction in elderly subjects, and calculation of ejection fraction from mitral ring motion will overestimate it in young subjects.