Early cardiovascular changes evoked by pressure overload (PO) may reveal adaptive strategies that allow immediate survival to the increased hemodynamic load. In this study, systolic and diastolic Ca²⁺ cycling was analyzed in left ventricular rat myocytes before (day 2, PO-2d group) and after (day 7, PO-7d group) hypertrophy development following aortic constriction, as well as in myocytes from time-matched, sham-operated rats. Ca²⁺ transient amplitude was significantly augmented in PO-2d. In PO-7d, diastolic [Ca²⁺]_i was reduced and mechanical twitch relaxation (but not [Ca²⁺]_i decline) was slowed. In PO groups, fractional sarcoplasmic reticulum (SR) Ca²⁺ release at a twitch, SR Ca²⁺ content, diastolic SR Ca²⁺ loss and SR-dependent, integrated Ca²⁺ flux during twitch relaxation were significantly greater than in sham-operated groups, whereas the relaxation-associated Ca²⁺ flux carried by the Na⁺-Ca²⁺ exchanger (NCX) was not significantly changed. In PO-7d, mRNA levels for cardiac isoforms of the SR Ca²⁺-ATPase (SERCA2a), phospholamban (PLB), calsequestrin, ryanodine receptor and NCX were not significantly altered, but the SERCA2a/PLB ratio was increased 2.5-times. Moreover, greater sensitivity to the inotropic effects of the -adrenoceptor agonist isoproterenol was observed in PO-7d. The results indicate that enhanced Ca²⁺ cycling between SR and cytosol takes place early after PO imposition, even before hypertrophy development. Increase in SR Ca²⁺ uptake may contribute to both enhancement of excitation-contraction coupling (augmented SR Ca²⁺ content and release) and protection against arrhythmogenesis due to Ca²⁺ buildup in the cytosol during diastole.