Single and double ventricular extrastimuli (VE) delivered during sustained, uniform ventricular tachycardia (VT) are able to reset or terminate the tachycardia. The relation between the coupling intervals of single and double VE resetting VT and those terminating it was examined in 80 uniform, morphologically distinct VT occurring in 52 patients. Of the 80 tachycardias receiving single VE, 41 were reset and 8 terminated. The corrected coupling interval of single VE first causing resetting was 0.81 +/- 0.08 compared with 0.66 +/- 0.06 for termination (p less than 0.001). Forty-two tachycardias received double VE with 33 being reset and 13 terminating. The corrected coupling interval of double VE at which resetting was first seen was 0.86 +/- 0.08 compared with 0.73 +/- 0.05 for termination (p less than 0.001). If the longest corrected coupling interval causing resetting was greater than or equal to 0.75, then 7 of 34 tachycardias terminated with single VE and 13 of 31 terminated with double VE compared with only 1 of 46 terminating with single VE and 0 of 10 with double VE if resetting was not observed by a corrected coupling interval of 0.75 (p less than 0.01 and p less than 0.02, respectively). If the longest corrected coupling interval at which resetting occurred was greater than or equal to 0.75, the predictive value for VT termination was 21% with single VE and 42% with double VE compared with only 2% with single VE and none with double VE if resetting was not observed by this corrected coupling interval.(ABSTRACT TRUNCATED AT 250 WORDS)