CARDIAC DEPRESSANTS are little used in medicine, however, some are used to slow the heartbeat in tachycardias and a number of these are often analogues or derivatives of other drugs with optimized activity for this purpose in the heart (e.g. procainamide, quinidine) — these are dealt with under antiarrhythmic agents.

In addition to drugs in these classes, many drugs have the adverse effect of cardiac depression as a side-effect. This is particularly so with LOCAL ANAESTHETICS (e.g. lignocaine, procaine), which is a major reason why they are only used by local application. A number of other drugs, particularly chemotherapeutic agents that have strong reasons for their selection, may be cardiac depressants in some patients at high doses (e.g. doxorubicin, quinine). Many drugs with depressant actions on the CNS are also cardiac depressant in higher doses (e.g. carbamazepine. chlorpromazine, pentobarbitone). Drugs with actions on the autonomic system may have cardiac depressant actions (e.g. bretylium, reserpine) Also, β-adrenoceptor antagonists, whose actions are generally beneficial, can in some conditions and in overdose cause heart block or even cardiac arrest. Cholin-oceptor muscarinic agonists, by definition, will have negative inotropic and chronotropic actions, and rarely methacholine is used in the emergency treatment of supraventricular tachycardias. See MUSCARINIC CHOLINOCEPTOR AGONISTS.