In order to study the relationship between 5-HT and ischemic ventriculararrhythmia we observed the effects of exogenous 5-HT on MAP and ECG of rats withischemic myocardium. The conclusion was that: (1) 5-HT increased the number of VEand prolonged the duration of VT and VF in DVA phase of rats with ischemic myocar-dium. But it could not produced the ventricular arrhythmia on rats without ischemic my-ocardium。(2) The effects of 5-HT mentioned in (1) was attributed to decreased Vmaxand MAPA of ischemic myocardium by 5-HT but it was not due to prolongation ofMAPD.