Figure 1. Morphology and functional impairment of CTSL-deficient (ctsl^–/–) hearts. A) Cross-sections (below heart valves) of wild-type (ctsl^+/+) and CTSL-deficient (ctsl^–/–) mouse ventricles from 2-month-old mice. B) Length of left ventricle (LV) in vivo determined by echocardiography in ctsl^+/+ and ctsl^–/– hearts at 2 and 12 mo of age. C) Cross-sections (below heart valves) of ctsl^+/+ and ctsl^–/– mouse ventricles from 12-month-old mice. Arrow marks a representative example of the 25% of hearts that develop pronounced dilation of LV and right ventricle (RV). D) Echocardiographic assessment of fractional shortening, a parameter for heart myocardial contraction in 2- and 12-month-old ctsl^–/– mice. E) mRNA expression of the natriuretic peptides ANP and BNP in ventricular myocardium of 2-month-old mice determined by quantitative, real-time RT-PCR. n.s. = not significant; **P < 0.01, ***P < 0.001 by Student’s t test.