* pregnant or breastfeeding women * symptoms or signs of acute myocardial ischemia * sinoatrial (sa) and atrioventricular (av) nodal block/dysfunction * symptoms or signs of atrial fibrillation/atrial flutter * history of hypotension * history of severe hypertension not adequately controlled with anti-hypertensive medications (systolic blood pressure ≥ 200 mmhg and/or diastolic blood pressure ≥ 110 mmhg) * severe renal impairment defined as glomerular filtration rate (gfr) \< 30 ml/min * history of clinically overt stroke within the past 3 years * history of seizure disorder * pre-existing asthma or chronic obstructive pulmonary disease * chronic anti-coagulation or anti-platelet therapy that would preclude surgery (prophylactic aspirin is acceptable) * 12.treatment within 30 days with hydroxychloroquine (hcq) or azithromycin * treatment with janus kinase inhibitors * treatment with theophylline or aminophylline within 12 hours of study dosing * treatment with persantine and/or aggrenox within 5 days * other clinical conditions that in the opinion of the investigator would make the subject unsuitable for the study

* pregnant or breastfeeding women * symptoms or signs of acute myocardial ischemia * sinoatrial (sa) and atrioventricular (av) nodal block/dysfunction * symptoms or signs of atrial fibrillation/atrial flutter * history of hypotension * history of severe hypertension not adequately controlled with anti-hypertensive medications (systolic blood pressure ≥ 200 mmhg and/or diastolic blood pressure ≥ 110 mmhg) * severe renal impairment defined as glomerular filtration rate (gfr) \< 30 ml/min * history of clinically overt stroke within the past 3 years * history of seizure disorder * pre-existing asthma or chronic obstructive pulmonary disease * chronic anti-coagulation or anti-platelet therapy that would preclude surgery (prophylactic aspirin is acceptable) * 12.treatment within 30 days with hydroxychloroquine (hcq) or azithromycin * treatment with janus kinase inhibitors * treatment with theophylline or aminophylline within 12 hours of study dosing * treatment with persantine and/or aggrenox within 5 days * other clinical conditions that in the opinion of the investigator would make the subject unsuitable for the study

- pregnant or breastfeeding women - symptoms or signs of acute myocardial ischemia - sinoatrial (sa) and atrioventricular (av) nodal block/dysfunction - symptoms or signs of atrial fibrillation/atrial flutter - history of hypotension - history of severe hypertension not adequately controlled with anti-hypertensive medications (systolic blood pressure ≥ 200 mmhg and/or diastolic blood pressure ≥ 110 mmhg) - severe renal impairment defined as glomerular filtration rate (gfr) < 30 ml/min - history of clinically overt stroke within the past 3 years - history of seizure disorder - pre-existing asthma or chronic obstructive pulmonary disease - chronic anti-coagulation or anti-platelet therapy that would preclude surgery (prophylactic aspirin is acceptable) - 12.treatment within 30 days with hydroxychloroquine (hcq) or azithromycin - treatment with janus kinase inhibitors - treatment with theophylline or aminophylline within 12 hours of study dosing - treatment with persantine and/or aggrenox within 5 days - other clinical conditions that in the opinion of the investigator would make the subject unsuitable for the study

- pregnant or breastfeeding women - symptoms or signs of acute myocardial ischemia - sinoatrial (sa) and atrioventricular (av) nodal block/dysfunction - symptoms or signs of atrial fibrillation/atrial flutter - history of hypotension - history of severe hypertension not adequately controlled with anti-hypertensive medications (systolic blood pressure ≥ 200 mmhg and/or diastolic blood pressure ≥ 110 mmhg) - severe renal impairment defined as glomerular filtration rate (gfr) < 30 ml/min - history of clinically overt stroke within the past 3 years - history of seizure disorder - pre-existing asthma or chronic obstructive pulmonary disease - chronic anti-coagulation or anti-platelet therapy that would preclude surgery (prophylactic aspirin is acceptable) - 12.treatment within 30 days with hydroxychloroquine (hcq) or azithromycin - treatment with janus kinase inhibitors - treatment with theophylline or aminophylline within 12 hours of study dosing - treatment with persantine and/or aggrenox within 5 days - other clinical conditions that in the opinion of the investigator would make the subject unsuitable for the study