CaMKIIδ plays a pivotal role in the regulation of cardiac excitation-contraction coupling. Work by ourselves and others suggests that CaMKIIδ is elevated in hypertrophy and heart failure (HF). However, it is unclear whether this elevation correlates with progression of heart failure. This study compares CaMKIIδ protein levels and enzyme activity at two separate time points (8 weeks and 32 weeks) following coronary artery ligation (under anaesthesia) of rabbit hearts. Basal left ventricular homogenates (LVHs) were used for global CaMKIIδ protein determination and activity assays. Sarcoplasmic reticulum (SR) preparations were also studied from the 8 week animals to measure localised CaMKIIδ expression and activity. CaMKIIδ protein expression was measured by quantitative immunoblotting using a CaMKIIδ-specific polyclonal antibody (Abgent) and signals were normalised to GAPDH. Low n numbers (n=6) were used to specifically identify whether significant changes could be detected early at both time points. In the 32 week model CaMKIIδ protein is significantly elevated in HF vs sham (0.11±0.01 vs 0.08±0.012, p=0.011) whereas in the 8 week model using similarly low n numbers there is no detectable change in CaMKIIδ (HF, 0.118±0.053 vs sham, 0.117±0.036). This contrasts with SR-associated CaMKIIδ expression which is significantly elevated in the 8 week model (~2.5-fold HF c.f. sham). CaMKIIδ activity in the same LVHs was then measured using an assay kit (Upstate). In the 32 week model using similarly low n numbers as before, CaMKIIδ activity was significantly up-regulated in HF vs sham (0.52±0.14 vs 0.4±0.11 pmol phosphate incorporated/min/μg total protein, p=0.009). At 8 weeks, although CaMKIIδ activity associated with the SR was significantly increased (HF, 0.84±0.18 vs sham, 0.35±0.05), initial activity measurements from LVHs show no significant change (HF, 0.63±0.15 vs sham, 0.53±0.18, n=3). These results suggest that differences may exist between local (SR) and global measurements of CaMKIIδ from the same experimental group. They also suggest the extent of increase in global CaMKIIδ expression and activity in LVHs is associated with the duration of heart failure.