The most important characteristic of calcium channels is a selective regulation of a slow incoming current of calcium into the tissue cells with tendency of a slow growth of the action potential. Such tissues include smooth muscles of the blood vessels, cardiocities and hearth noduses (AVand SAnode). Different calcium antagonists have different influences on the mentioned tissues, because they also have different chemical components. Verapamil, Nifedipin and Diltiazem have the most common usage. Verapamil is a product of papaverine, nifedipin is a product of dehydroperidine while diltiazem is a product of benzodiazepine. Their common characteristic is blocking the calcium channels which cause blood vessels vasodilatation, negative inotropic and negative chronotropic influence. By blocking calcium to enter through channels spores of miofibrile smooth muscles, calcium antagonists are reducing the amount of available calcium for contraction, which causes vasodilatation. One of the best-known and the commonest calcium antagonist is verapamil. In electrophysiological terms, it inhibits action potential of the heart noduses (especially AV node), where the most important thing for depolarisation, is a slow entrance of calcium. By extending the refractory period of SA node, it reduces the frequency of impulse generation (heart frequency), while by extending the refractory period of AVnode, it slows down the work of chambers in cases of flater and atrium fibrillation. Taking into consideration the fact that verapamil shows cardiodepresive effects, the aim of our work is to study closely its effects on electrocardiogram and hemodynamic parameters. The experiment was conducted on six adult, healthy dogs which were, after 10 minutes 0,9% NaCl infusion, treated with i.v. bolus verapamil injections on every 5 minutes until the appearance of intoxication signs, which causes bradycardia, heart rhythm disorder and the fall of arterial blood pressure. The average verapamil dose was 4 mg per kilogram. After i.v. verapamil administration, heart frequency and middle arterial pressure have a significant fall, while central venous pressure has a significant rise. Larger verapamil doses nd rd can significantly extend T-P and P-R interval with the appearance of AV-block (2 and 3 grade), while the Q-T interval doesn't show any significant change.

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