these data are consistent with the hypothesis that exercise-induced tachycardia results largely from beta 1-receptor activation that is blocked by both cardioselective and nonselective drugs , whereas isoproterenol activates both beta 1- and beta 2-receptors so that after cardioselective blockade there remains a beta 2-component that can be blocked with a nonselective drug .
C0039231
tachycardia
C0022245
isoproterenol