The myocardial disposition and pharmacodynamics of propafenone were studied in 10 normal and 10 norepinephrine-induced cardiomyopathic rabbit hearts. The left ventricular propafenone concentrations measured after perfusion of propafenone (0.3 microM) for 150 min were similar in the normal group (18 +/- 8 micrograms/g) compared to the cardiomyopathy group (20 +/- 5 micrograms/g, P = NS). However, the concentration of propafenone in cardiomyopathic left ventricular papillary muscle, which was always extensively involved in the inflammatory process, was significantly lower (11 +/- 2 micrograms/g) compared to normal papillary muscle (19 +/- 4 micrograms/g, P less than .05). During propafenone perfusion a significantly greater increment in ventricular conduction time was observed in the cardiomyopathy group (17 +/- 6 msec) compared to the normal group (12 +/- 3 msec, P less than .05). The propafenone myocardial concentration-effect relationships describing changes in QRS duration were shifted to the left in the cardiomyopathy group. Furthermore, the slopes of these linear concentration-effect relationships were greater in the cardiomyopathy group (1.80 +/- 0.60 msec/micrograms/g) compared to the normal group (1.07 +/- 0.25 msec/micrograms/g, P less than .01). The ventricular effective refractory period was shorter at base line in the cardiomyopathy hearts (156 +/- 21 msec) compared to the normal group (176 +/- 23 msec, P less than .08). However, propafenone effects on changes in the ventricular effective refractory period were similar in the two groups. Thus, the myocardial accumulation of propafenone is reduced in areas of extensive necrosis observed in norepinephrine-induced cardiomyopathy. As well, cardiomyopathic tissue is more responsive to propafenone effects on ventricular conduction time.