Fig. 5.

Significant reductions in cardiac reserve of aged mdx hearts. In a variety of measures of global cardiac function the 9-mo-old mdx show limited response to dobutamine stimulation. In C57BL/10 mice there are significant changes in cardiac output (A), stroke work (B), stroke volume (C), heart rate (D), end-systolic volume (E), and ejection fraction (F). The hearts of mdx mice show either no change or only with the highest dose of dobutamine. Specifically, mdx hearts have significantly lower cardiac output and stroke work following dobutamine stimulation. *P < 0.05, difference from baseline C57BL/10. †P < 0.05, difference from baseline mdx. ‡P < 0.05, difference from C57BL/10 at that dose.