The transverse aortic constriction (TAC) mouse model is widely used to study pressure overload–induced cardiac remodeling. But simply producing left ventricular hypertrophy is not enough for many drug-development programs.

The more important question is: how does the phenotype evolve over time, and when does the model transition from compensated hypertrophy toward ventricular dilation and cardiac dysfunction?

We recently completed a longitudinal TAC study in male C57BL/6J mice designed to characterize that progression over an eight-week period. Serial echocardiography provided a clear view of the transition from early pressure-overload hypertrophy through increasingly maladaptive remodeling.

Establishing the pressure load
Two weeks after TAC, Doppler measurements confirmed substantial aortic constriction. TAC vehicle animals had a mean pressure gradient of approximately 76 mmHg, compared with approximately 3 mmHg in sham-operated animals.
Importantly, all evaluable TAC vehicle animals exceeded a 40-mmHg pressure-gradient threshold.
At this early stage, the phenotype was predominantly one of concentric hypertrophy. LV mass was already approximately 40% greater than sham, while ejection fraction remained relatively preserved.
This creates a potentially useful therapeutic intervention window: substantial pressure overload and hypertrophy are already present, but overt ventricular dilation and systolic dysfunction have not yet fully developed.

Progression toward maladaptive remodeling
The phenotype continued to evolve over the following weeks.
By approximately four weeks after TAC, LV hypertrophy remained prominent and chamber volumes began to increase. Systolic function was beginning to separate from sham, while changes in indices of diastolic function were also becoming apparent.
By six weeks, chamber dilation had become a major component of the phenotype. End-systolic volume was approximately twice that observed in sham animals, and ejection fraction had declined to approximately 46%.
At eight weeks, the model showed clear evidence of decompensated remodeling:

Terminal measurements supported the imaging findings. LV plus septal weight normalized to tibia length was increased by approximately 81%, with accompanying increases in RV and lung weight indices.

Taken together, the longitudinal data describe a recognizable progression:
pressure overload → concentric hypertrophy → chamber dilation → systolic and diastolic dysfunction
Demonstrating model responsiveness

Model characterization is considerably more useful when the phenotype can also be modified with an established pharmacologic intervention.
Enalapril was therefore included as a positive control.
By the later stages of the study, enalapril produced broad improvements relative to untreated TAC animals. At eight weeks, effects included approximately:

Terminal LV, RV and lung weight indices were also reduced.

One important consideration is that enalapril treatment began before TAC in this particular characterization study. These findings therefore demonstrate model responsiveness and attenuation of disease development, rather than reversal of an already established phenotype following delayed treatment initiation.
That distinction matters when designing therapeutic studies.

Why longitudinal characterization matters
For programs targeting cardiac hypertrophy or progression toward heart failure, the timing of treatment can be just as important as the model itself.
In our recent dataset, the disease stages were reasonably well separated:
~2 weeks: established hypertrophy with largely preserved systolic function
~4 weeks: compensated remodeling with emerging dysfunction
~6 weeks: transition toward ventricular dilation
~8 weeks: decompensated remodeling with clear systolic and diastolic abnormalities

That provides flexibility to evaluate therapies at different points in the disease process—from prevention or attenuation of hypertrophy to intervention during the transition toward ventricular dysfunction.

It also illustrates why relying on a single terminal measurement can miss much of the biology of the TAC model. Serial echocardiography allows each animal to be followed through the remodeling process and provides insight into when a treatment begins to alter disease trajectory, not simply whether the heart looks different at termination.

At CorDynamics, we continue to refine cardiovascular disease models around that principle: combining robust surgical models with longitudinal imaging and physiologic measurements to understand not only whether a therapy works, but where in the progression of disease it exerts its effect.