1 The present study compared the cardiovascular eects of mibefradil (MIB), a novel Ca 2+ -channel antagonist with high selectivity for T-type Ca 2+ -channels to the eect of the L-type Ca 2+ -channelantagonists nifedipine (NIF) and diltiazem (DIL) in left ventricular myocardium and coronary arteries of hearts obtained from patients suering from dilated cardiomyopathy (NYHA IV). Right atrial myocardium from patients undergoing aortocoronary bypass surgery without signs of cardiac failure was studied as well. 2 NIF and DIL (100 mmol l 71 ) completely depressed force of contraction (FOC) in electrically driven left ventricular myocardium (NIF 6.5+1.4% and DIL 7.1+1.2% of control), whereas a similar concentration of MIB only reduced force of contraction to 55.1+4.0% of the basal FOC. The negative inotropic potency as measured by the concentration needed to reduce basal FOC for 25% was NIF (0.0095 mmol l ). 6 The vasoselectivity measured by the ratio of the concentration needed to achieve a 25% decrease in force and the concentration needed for 25% vasodilatation was 316 for MIB, 1.5 for NIF and 1.0 for DIL. 7 The present study provides evidence that blockade of T-type Ca 2+ -channels (e.g. mibefradil) results in potent vasodilatory properties with only minor cardiodepressant eects.

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