Slow coronary flow is an angiographic phenomenon characterized by delayed opacification of vessels in the absence of any evidence of obstructive epicardial coronary disease. In this article, we present serious clinical manifestations of extremely slow coronary flow in two hypertensive patients with preserved ejection fraction in echocardiographical examination: a 57 year-old woman with acute coronary syndrome and temporary ST elevation; and a 65 year-old man with atrial tachycardia which was leading to sudden arrest of circulation. The woman was admitted to hospital due to recurrent syncope and chest pain. Because of severe bradycardia, an AAI pacemaker was implanted. Coronary angiography without evident obstructive lesion revealed extremely slow flow of dye through arteries. The man was admitted to hospital because of heart palpitations (paroxysmal atrial tachycardia, PAT) followed by chest pain. During hospitalization, a sudden arrest of circulation in the course of supraventricular tachycardia of 220/min with atrioventricular conduction of 1:1 occurred. Coronary arteriography did not show any occlusions in the coronary arteries, although extremely slow dye flow was seen. Electrophysiological examination revealed arrhythmia of the left atrial (PAT) (tricuspid valve anulus mapping) without induced ventricular arrhythmia. Because of symptomatic bradyarrhythmia, a VVI heart pacemaker was implanted. Over a 12-month observation, his heart rate remained under control, and the patient did not complain of chest pains or heart palpitations.