This brief review addresses itself to the following questions on normal and hypertrophied muscle. 1) What changes, if any, take place in the mechanical properties of cardiac muscle during pressure and volume overload hypertrophy? 2) What parameters may signal preoperatively irreversibility of hypertrophy and chamber enlargement? 3) Are the effects of age and hypertrophy on muscle stiffness similar? 4) What relationships exist between diastolic properties and systolic function? The analyses of the elastic properties of cardiac muscle based on several animal and clinical studies indicate that: a) Muscle stiffness in pressure overload is elevated and is normal in volume overload in the majority of the animal studies. However, the clinical studies support the hypothesis that muscle stiffness remains normal in mild to moderate degrees of valvular disease and is elevated in severe valvular disease. b) Wall stress, volume:mass, and radius:thickness ratios are useful prognostic indicators regarding reversibility of wall hypertrophy and/or chamber enlargement. c) Effects of age and hypertrophy on muscle stiffness are similar for the age range of young adult (6 mo) to old (90 wk) SHR and WKY rats. d) Increased muscle stiffness is invariably accompanied by decreased muscle shortening velocity but rate of force development and peak force may not be impaired.