Various embodiments concern sensing a first signal indicative of a plurality of different phases of a cardiac cycle with a sensor and sensing a second signal with an ultrasound sensor within the heart over different phases, the second signal indicative of the density of a section of cardiac tissue. Each phase can be associated with an indication of the density of the section of cardiac tissue during the phase based on the second signal. It can be determined whether the section of cardiac tissue compressed during the cardiac cycle based on a change in the indication of density of the cardiac tissue over the plurality of different phases. The efficacy of ablation therapy can be evaluated based on the compressibility of the section of cardiac tissue.
