Frequency-dependent depression of myocardial contractility by slow calcium channel blocking drugs

The negative inotropic effects of two dihydropyridine and two non-dihydropyridine calcium slow channel blocking drugs were studied using ferret isolated papillary muscle preparations contracting both isotonically and isometrically. The degree of inotropic depression was found to be dependent on the frequency of stimulation for all four agents. Frequency dependence of inotropic effect was of the order: nifedipine less than felodipine less than diltiazem less than verapamil.