Heterocyclic are provided which are sodium/proton exchange (NHE) inhibitors which have the structure ##STR00001## wherein n is 1 to 5; X is N or C--R.sup.5 wherein R.sup.5 is H, halo, alkenyl, alkynyl, alkoxy, alkyl, aryl or heteroaryl; Z is a heteroaryl group, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are as defined herein, and where X is N, R.sup.1 is preferably aryl or heteroaryl, and are useful as antianginal and cardioprotective agents. In addition, a method is provided for preventing or treating angina pectoris, cardiac dysfunction, myocardial necrosis, and arrhythmia employing the above heterocyclic derivatives.