What is the effect of glycoside plants on heart rate?

Glycoside plants, such as those containing cardenolides or bufadienolides, are known to have a significant impact on heart function, primarily through their action on the heart muscle and conduction system. The primary effect of these compounds is to increase the force of cardiac contraction through their inhibition of the sodium-potassium ATPase pump, leading to increased intracellular calcium levels. This enhancement of contractility can lead to an increased force of heart contractions but often comes with a decreased heart rate, due to their vagotonic effects.

The decrease in heart rate occurs through various mechanisms, including increased vagal tone and decreased sympathetic output. The activation of the parasympathetic nervous system results in bradycardia, which is characterized by a slower heart rate. This is particularly notable when glycosides are used therapeutically, such as in the treatment of certain heart conditions like atrial fibrillation or heart failure, where control of heart rate is beneficial.

While glycosides can lead to irregular heart rates, especially at toxic levels, the primary, direct effect is a reduction in heart rate through bradycardia. This characteristic ties strongly to their pharmacological properties and expected clinical outcomes when administered.