Calcitonin gene-related peptide (CGRP) is a potent vasodilator, but its effects on in situ ventricular function are unknown. We studied effects of intracoronary CGRP (100, 200, and 600 pmole/min, for 10 min) in 21 open-chest chloralose-anesthetized dogs. Systemic, pulmonary, left ventricular (LVP), central venous, and pulmonary capillary wedge pressures were continuously monitored. Left ventricular wall thickness (WT) and circumflex coronary blood flow were also measured. CGRP was infused into the proximal circumflex artery. During CGRP infusion there were no changes in heart rate, cardiac index, pulmonary artery pressure, or systemic vascular resistance, no percentage change in ventricular WT, and no changes in dWT/dt, peak dP/dt, or the slope of end-systolic points on WT/LVP loops. But there were significant changes in coronary flow (CQ), coronary resistance (CRES) and mean arterial blood pressure (MAP) from control (C)* (P less than 0.05). (table; see text) CGRP is a potent coronary artery vasodilator causing notable dose-dependent decreases in coronary resistance and a rise in myocardial flow, despite a decreased MAP (all P less than 0.05). CGRP does not affect ventricular contractility in vivo.