Abstract： Background Many basic and clinical studies have proved that anisodamine can produce significant effect on relieving microvascular spasm, improving and dredging the coronary microcirculation. It may be beneficial to the improvement of slow-reflow phenomenon (SRP) following percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI).So we investigated the effect of intracoronary administration of anisodamine on SRP of infarct related artery (IRA)following primary PCI in patients with ST segment elevated acute myocardial infarction (STEAMI).Methods Twenty-one patients with SRP from a total of 148 STEAMI patients accepted primary PCI were enrolled into this study from September 2004 to December 2005. When SRP happened, nitroglycerin (200 μg) was "bolus" injected firstly into IRA to exclude the spasm of epicardial artery and identify SRP as well as a baseline and self-control agent following PCI. Ten minutes later, 1000 μg of anisodamine was injected into IRA with SRP at 200 μg/s, while the coronary angiography (CAG) was taken before and at 1st, 3rd and 10th minute after administration of nitroglycerin or anisodamine,respectively. The corrected TIMI frame count (cTFC), TIMI myocardial perfusion grade (TMPG) and the diameter of IRA were calculated and analyzed by Gibson's TIMI frame count method using quantitative computer angiography (QCA)system to evaluate the influence of anisodamine on coronary flow and vessel lumen. In the meantime the invasive hemodynamic parameters of intracoronary and systemic artery (systolic, diastolic and mean pressure) and electrocardiogram (ECG) were measured and monitored. The changes of ventricular performance parameters and the adverse reaction were evaluated and followed-up at 1 month post-PCI.Results No significant changes in cTFCs and TMPGs were found at 1st, 3rd and 10th minute after intracoronary administration of nitroglycerin as compared with the baseline control (P＞0.05). cTFCs were decreased by 58.3%, 56.2%,and 54.6%, respectively (P＜0.001), and TMPGs were increased from 1.13±0.21 grade to 2.03±0.32, 2.65±0.45 and 2.51±0.57 grades (P＜0.05) at 1st, 3rd and 10th minute after intracoronary administration of anisodamine as compared with those after intracoronary administration of nitroglycerine, respectively. The average coronary blood flow of TIMI grade was improved from 1.76±0.43 to 2.71±0.46 (P＜0.05) while the diameter of middle segment in re-patented coronary artery was slightly increased from (3.20±0.40) mm to (3.40±0.50) mm at the 3rd minute after intracoronary administration of anisodamine (P＞0.05) as compared with those of nitroglycerine control. The systolic, diastolic and mean pressures of intracoronary artery after intracoronary administration of anisodamine increased from 115 to 123, 75 to 84, 88 to 95 mmHg (P＜0.05), respectively, along with the rise of heart rate from 68 to 84 beats per minute (P＜0.05). There were no significant changes in intervals of PR, QT and QRS (P＞0.05) and no any severe fast arrhythmia after intracoronary administration of anisodamine. The ventricular performance parameters were significantly improved and no major adverse cardiovascular events (MACE) were found during follow-up at 1 month post-PCI.Conclusions Intracoronary administration of 1000 μg anisodamine is effictive in reversing SRP following PCI in STEAMI patients, especially it is suitable for SRP patients with bradycardia or hypotension.