Prinoxodan (RG W-2938) is a new nonglycoside, noncatecholamine cardiotonic/vasodilator agent is examined in vivo in anesthetized and conscious dogs. Prinoxodan 30-300 μg/kg administered intravenously (i.v.) to anesthetized dogs increases contractile force while decreasing arterial pressure and total peripheral resistance (TPR) in a dose-related manner. Heart rate (HR) is only slightly increased, and aortic flow is not appreciably altered. A single oral dose of Prinoxodan 0.3 mg/kg administered to conscious chronically instrumented dogs produces a marked and sustained increase in contractility 15-240 min after treatment while only slightly increasing HR. The effects of Prinoxodan 30-300 μg/kg, i.v. are studied in a mecamylamine-propranolol-induced model of heart failure. Prinoxodan effectively reverses the drug-induced heart failure by increasing myocardial contractility and decreasing arterial pressure while only slightly affecting HR^[2].