This study investigates the effects of adenosine on human coronary circulation, both intracoronary and intravenously. Adenosine is a potent vasodilator used in animal studies but has been limited in human use due to safety concerns. The researchers administered adenosine in various doses to 39 patients to measure coronary blood flow velocity (CBFV), systemic hemodynamics, and electrocardiogram (ECG) changes. Intracoronary boluses of 16 μg or more (12 μg in the right coronary artery) caused maximal coronary hyperemia, similar to papaverine. Intracoronary infusions at 80 μg/kg/min or higher also induced maximal hyperemia. Intravenous infusions at 140 μg/kg/min caused near-maximal coronary hyperemia in most patients, with minimal changes in systemic hemodynamics and no significant ECG changes. The study suggests that adenosine is a safe and effective agent for inducing coronary hyperemia in humans, with advantages over existing methods such as papaverine and dipryidamole. However, potential methodological issues, such as measurement techniques and patient selection, are discussed, and further studies are recommended to explore adenosine's safety and efficacy in different patient populations.This study investigates the effects of adenosine on human coronary circulation, both intracoronary and intravenously. Adenosine is a potent vasodilator used in animal studies but has been limited in human use due to safety concerns. The researchers administered adenosine in various doses to 39 patients to measure coronary blood flow velocity (CBFV), systemic hemodynamics, and electrocardiogram (ECG) changes. Intracoronary boluses of 16 μg or more (12 μg in the right coronary artery) caused maximal coronary hyperemia, similar to papaverine. Intracoronary infusions at 80 μg/kg/min or higher also induced maximal hyperemia. Intravenous infusions at 140 μg/kg/min caused near-maximal coronary hyperemia in most patients, with minimal changes in systemic hemodynamics and no significant ECG changes. The study suggests that adenosine is a safe and effective agent for inducing coronary hyperemia in humans, with advantages over existing methods such as papaverine and dipryidamole. However, potential methodological issues, such as measurement techniques and patient selection, are discussed, and further studies are recommended to explore adenosine's safety and efficacy in different patient populations.