Effects of metoprolol and ramipril on action potentials after myocardial infarction in rats.

The effects of chronic treatment with the beta-adrenoceptor antagonist metoprolol, the angiotensin converting enzyme inhibitor ramipril, their combination, or placebo on action potential configuration 6 weeks after myocardial infarction in rats were studied. Action potentials were measured in isolated left ventricular posterior papillary muscles and compared with action potentials from a sham operated group without infarction. After infarction, the action potential amplitude was reduced and this phenomenon was partially reversed by metoprolol- and ramipril-treatment. Prolonged repolarisation after infarction compared to sham operated animals was additionally delayed after metoprolol treatment. Thus, metoprolol extends the refractory period, which may counteract tachyarrhythmia.