Previous studies have shown that myocytes isolated from sedentary (Sed) rat hearts 3 wk after myocardial infarction (MI) undergo hypertrophy, exhibit altered intracellular Ca(2+) concentration ([Ca(2+)](i)) dynamics and abnormal contraction, and impaired sarcoplasmic reticulum (SR) function manifested as prolonged half-time of [Ca(2+)](i) decline. Because exercise training elicits positive adaptations in cardiac contractile function and myocardial Ca(2+) regulation, the present study examined whether 6-8 wk of high-intensity sprint training (HIST) would restore [Ca(2+)](i) dynamics and SR function in MI myocytes toward normal. In MI rats, HIST ameliorated myocyte hypertrophy as indicated by significant (P </= 0.05) decreases in whole cell capacitances [Sham-Sed 179 +/-12 (n = 20); MI-Sed 226 +/- 7 (n = 20); MI-HIST 183 +/- 11 pF (n = 19)]. HIST significantly (P < 0.0001) restored both systolic [Ca(2+)](i) [Sham-Sed 421 +/- 9 (n = 79); MI-Sed 350 +/- 6 (n = 70); MI-HIST 399 +/- 9 nM (n = 70)] and half-time of [Ca(2+)](i) decline (Sham-Sed 0. 197 +/- 0.005; MI-Sed 0.247 +/- 0.006; MI-HIST 0.195 +/- 0.006 s) toward normal. Compared with Sham-Sed myocytes, SR Ca(2+)-ATPase expression significantly (P < 0.001) decreased by 44% in MI-Sed myocytes. Surprisingly, expression of SR Ca(2+)-ATPase was further reduced in MI-HIST myocytes to 26% of that measured in Sham-Sed myocytes. There were no differences in calsequestrin expression among the three groups. Expression of phospholamban was not different between Sham-Sed and MI-Sed myocytes but was significantly (P < 0.01) reduced in MI-HIST myocytes by 25%. Our results indicate that HIST instituted shortly after MI improves [Ca(2+)](i) dynamics in surviving myocytes. Improvement in SR function by HIST is mediated not by increased SR Ca(2+)-ATPase expression, but by modulating phospholamban regulation of SR Ca(2+)-ATPase activity.