Catecholamines are important substances in the body and have the following main effects on the heart muscle: First, increase the heart rate. The epinephrine and norepinephrine in catecholamines can affect the ionic activity of autoregulatory cells such as the sinoatrial node, so that the frequency of the impulses issued by the autoregulatory cells increases and the heart rate increases. Secondly, the conduction between atria and ventricles is accelerated. Catecholamines can affect the inward flow of calcium ions in the atrioventricular node cells and increase the excitability of the atrioventricular node cells, so that the impulses generated by the sinus node can be conducted through the atrioventricular node at a faster rate. Third, increase the contractility of cardiomyocytes. Catecholamines can promote the opening of calcium channels in cardiomyocytes, leading to an increase in the concentration of calcium ions entering the cell from outside the cell, which is an important ion involved in the contraction of cardiomyocytes, leading to an increase in the contractility of cardiomyocytes.