Effects of ketamine on the cardiac papillary muscle of normal hamsters and those with cardiomyopathy. The effect of ketamine (10(-5) and 10(-4) M) on the intrinsic contractility of left ventricular papillary muscle from normal hamsters and those with cardiomyopathy (BIO 82.62, 6-month old) was investigated. At these concentrations, ketamine induced a positive inotropic effect on normal papillary muscle, as shown by an increase in maximum unloaded shortening velocity (+19 +/- 4 and +34 +/- 5%, P less than 0.05), active isometric force (+32 +/- 8 and +57 +/- 11%, P less than 0.05), and peak power output (+40 +/- 8 and +80 +/- 16%, P less than 0.05), and induced a slight decrease in sarcoplasmic reticulum function. Ketamine had no effect on the curvature of the total force-velocity curve, suggesting that it does not modify myothermal economy. Contractility of papillary muscle from hamsters with cardiomyopathy was less than that of controls, as shown by the decrease in isometric active force (-41%, P less than 0.02), peak power output (-33%, P less than 0.05), and sarcoplasmic reticulum function. The positive inotropic effect of ketamine on papillary muscle from hamsters with cardiomyopathy was less marked than in controls and almost suppressed in some cases: only the maximum unloaded shortening velocity was significantly increased with 10(-5) M ketamine (+7 +/- 6%, P less than 0.05), whereas no significant changes were observed in active isometric force (+14 +/- 8 and +13 +/- 11%; nonsignificant [NS]) and peak power output (+9 +/- 5 and +13 +/- 8%; NS) with ketamine (10(-5) and 10(-4) M, respectively). 