Effects of fluroxene and enflurane on myocardial mechanics of isolated papillary muscles obtained from cats with experimental congestive heart failure and from cats with normal hearts were compared. Significant impairment of myocardial performance, with elevated right ventricular pressure and reduced cardiac output, was observed in cats with congestive heart failure. At equipotent anesthetic concentrations (MAC in man) of fluroxene and enflurane, reductions of myocardial performance were similar in the two groups. When changes in maximal velocity of shortening (Vmax) and maximal developed force (Fm) in museles from hearts after congestive heart failure at MAC were compared with control values for normal hearts, depressions were 68 per cent and 70 per cent for fluroxene, and 72 per cent and 68 per cent for enflurane, respectively. These depressions, resulting from the combined effects of congestive heart failure and anesthetic, were similar to those caused by halothane and by isoflurane, but significantly greater than that caused by cyclopropane.