Enalapril increases cardiac refractoriness

The influence of enalapril--an angiotensin converting enzyme inhibitor--on cardiac refractoriness was investigated. Strength-interval curves were initially obtained under control conditions and after exposing the muscles to Tyrode solution containing 50 micrograms/ml of enalapril. The results indicate that enalapril displaced the strength-curves to the right. The minimal current intensity required to elicit a propagated response was clearly increased by enalapril at all the intervals used. No change in action potential duration was found with enalapril but the action potential amplitude and the resting potential were both increased. The rise in cardiac refractoriness caused by enalapril might indicate that the drug has anti-arrhythmic properties.