The aim of this study was to determine whether the effect of caffeine on calcium (Ca²⁺) transients in isolated perfused rat cardiomyocytes is age-related. Caffeine is known to induce Ca²⁺ release from the sarcoplasmic reticulum (SR) (O’Neill SC, Eisner DA., 1990). Whether this effect of caffeine is the same in all age groups postnatally, is not presently known. Cardiomyocytes were enzymatically isolated from 14, 21, 28 days old and adult rat hearts. Freshly isolated cardiomyocytes were loaded with the Ca²⁺ fluorescent dye Fura-2, then perfused with HEPES buffer (1mM Ca²⁺) in a chamber under an inverted microscope at 34^οC and stimulated at 0.2Hz. After equilibration cardiomyocytes were perfused with 20mM caffeine for 1 minute followed by washing with normal buffer. Ca²⁺ transients were monitored using photometry throughout. Data is expressed as mean ± standard error. Exposure of adult cardiomyocytes to caffeine induced the characteristic marked increase in Ca²⁺ transient amplitude that was followed by complete abolition of the transients indicating emptying of the SR of Ca²⁺. This effect was also seen in cardiomyocytes from all other age groups. Upon reperfusion and washing out the caffeine, the SR gradually refills its Ca²⁺ stores and normal transients are restored. The rate of SR refilling was significantly slower in 14 day cardiomyocytes compared to those from adult (ANOVA, p= 0.027, n=10). The 14 day old cardiomyocytes on average took approximately 172 ± 12 seconds to refill the SR in comparison to adult cardiomyocytes which took 120 ± 10 seconds when exposed to the same concentration of caffeine for the same duration of time. This work shows an age-related difference in rate of SR refilling following caffeine induced emptying. This could be due to difference in SR development. Additionally, refilling of the SR with Ca²⁺ in early postnatal development depends on extracellular Ca²⁺ coming via the Na⁺/Ca²⁺ exchanger rather than the Ca²⁺ channel (Artman, M., 1992). The exchanger is likely to be slower in transporting Ca²⁺ across the sarcolemma which would explain the slower rate of SR refilling.