RWJ-29009, (6S)-trans(-)-l-(6(7-dihydro-6-hydroxy-5,5-dimethyl-2-nitro-5 /f-thieno[3,2-b]pyran-7-y1)-2-piperidinone, is a structurally novel and extremely potent potassium channel activator that may be useful for treatment of hypertension and ischemic heart disease. We assessed the cardiovascular profile of RWJ 29009 in anesthetized and conscious dogs. RWJ 29009 (0.1–2 μg/kg intravenously, i.v.) dose-relatedly increased coronary blood flow (CBF) and decreased arterial pressure in anesthetized dogs. Total peripheral resistance and coronary vascular resistance were concurrently reduced without significant changes in heart rate (HR) or cardiac output (CO). Left ventricular (LV) dPldtmax and myocardial contractile force were decreased only at the highest dose of 10 μg/kg. Cromakalim (3–100 μg/kg), although much less potent, had a qualitatively similar profile. Glyburide pre-treatment (5 mg/kg i.v.) shifted the dose response of RWJ 29009 for increasing CBF and decreasing arterial pressure to the right. The dose responses of cromakalim were similarly shifted to the right, whereas the effects of nifedipine on CBF and arterial pressure were not affected by glyburide. RWJ 29009 (0.3 and 1 μg/kg) had no effect on myocardial O2 consumption (MVO2) except for a transient increase immediately after administration of 1 μ.g/kg. MVO2 returned to control 15 min after dosing, although CBF remained significantly increased. In conscious dogs, RWJ 29009 (0.3–10 fig/kg, i.v. and orally, p.o.) produced dose-related increases in CBF and decreases in arterial pressure similar to those produced in anesthetized dogs, except that HR was increased concurrently. The i.v. and p.o. potency of RWJ 29009 were comparable, indicating high oral bioavailability. Thus, RWJ 29009 is an extremely potent coronary and peripheral vasodilator with a cardiovascular profile similar to that of other potassium channel activators. Like those of other potassium channel activators, its mechanism of action appears to involve activation of ATP-regulated potassium channels.