YS-201 (Diperdipine) markedly reduces systemic vascular resistance and improves stroke index and left ventricular ejection fraction. Mean pulmonary artery and wedge pressures are slightly increased as a possible consequence of enhanced venous return, whereas right atrial and left ventricular end-diastolic pressures are not significantly changed. Nevertheless, an increase in preload is clearly indicated by an augmented left ventricular end-diastolic volume index after administration of diperdipine. After intravenous and oral doses, absolute bioavailability is calculated to be 18.7%. Biliaryexcretion accounts for about 0.1% of the total clearance of diperdipine and does not contribute to the overall elimination of the drug. After intraportal administration, the bioavailable fraction of diperdipine is increasing up to 44.3% suggesting a prehepatic site of loss of the drug. The single application of diperdipine to mice and rats by gavage causes intolerance reactions starting at the lowest tested dose level of 200 mg/kg b.w. p.o. (mice) and at 250 mg/kg b.w. p.o. (rats). In the rat, toxic effects occur from 15 mg diperdipine/kg b.w./day p.o. onwards.