Tachyphylaxis to verapamil.
D000368:Aged; D006352:Heart Ventricles; D006801:Humans; D008297:Male; D013610:Tachycardia / Q000188:drug therapy*; D013618:Tachyphylaxis; D014700:Verapamil / Q000627:therapeutic use*
D014700:Verapamil