Enhanced expression and polymerization of tubulin during pressure overload severely contributes to development of cardiac failure because ventricular myocytes (vm) work against a higher stiffness (e.g. Ishibashi, 2003). Here we studied whether such a possibility also applies to the hypertrophied vm from old mice (25 months). In old vm, isotonic shortening reached smaller peaks (5% vs. 6.8% of cell length in young vm) and followed a slower time course (TTP 114±5 ms vs. 93±3 ms, time to 50% relaxation 188±8 ms vs. 154±3 ms). Since also Ca-transients showed smaller amplitudes and slower kinetics, the depressed contractility of old vm could result from their different Ca handling. Contractility of old vm might be hampered by the 2.4-fold higher apparent elastic modulus. The higher stiffness of old vm could be normalized by colchicine (depolymerizing tubulin) but not by cytochalasin D (depolymerizing actin). In young vm, stiffness increased 2-fold after preincubation with Taxol (enhancing tubulin polymerization). Different to pressure hypertrophy, hypertrophy due to aging did not increase the tubulin concentration, the ratio alpha tubulin over alpha actin was 7.6 in young and 7.1 in old vm. We conclude that aging increases polymerization status of tubulin and that the elevated vm stiffness contributes to the impaired contraction of the aged heart.