Each of three harmala alkaloids, harmine, harmaline, and harmalol, decreased heart rate and increased pulse pressure, peak aortic flow, and myocardial contractile force in intact normotensive anesthetized dogs. Harmine reduced systemic arterial blood pressure and total peripheral vascular resistance; harmaline-evoked decreases were frequently followed by a secondary increase; and the effects of harmalol on these two parameters were inconsistent.