Results: In the experiments on contractility of the left atria XT and Verapamil(Ver) significantly depressed the positive staircase phenomena, which was reversed by Ver but not by XT.

• 钙通道阻滞药维拉帕米对正阶梯现象的抑制作用较XT为强,并可使正阶梯现象翻转,但对静息后增强效应无明显影响。XT对哇巴因的正性肌力作用及随后出现的心肌收缩力降低的毒性反应均有明显的对抗作用。