Short-term effects of intravenous clonidine in congestive heart failure.

After intravenous bolus injections of clonidine HCl (150 micrograms) to 12 patients with congestive heart failure, peak effects appeared in 5 to 20 min. Clonidine reduced heart rate from 94 +/- 14 to 82 +/- 14 bpm (mean +/- SD, P less than 0.05), left ventricular filling pressure from 31 +/- 5 to 23 +/- 5 mm Hg (P less than 0.001), mean systemic arterial pressure from 98 +/- 13 to 82 +/- 13 mm Hg (P less than 0.001), mean pulmonary artery pressure from 46 +/- 6 to 38 +/- 6 mm Hg (P less than 0.001), and right atrial pressure from 14 +/- 5 to 11 +/- 5 mm Hg (P less than 0.05). Cardiac index increased from 1.6 +/- 0.4 to 1.8 +/- 0.6 l/min/m2 (P less than 0.05) and stroke volume from 32 +/- 10 to 43+/- 12 ml/beat (P less than 0.05). Systemic vascular resistance decreased from 2,342 +/- 800 to 1,795 +/- 345 dynes sec cm-5 (P less than 0.05) and pulmonary vascular resistance from 365 +/- 158 to 263 +/- 114 dynes sec cm-5 (P less than 0.05). We conclude that clonidine decreases heart rate and left ventricular preload and afterload in congestive heart failure.