Heart rate date normally used to date pregnancy in the medical community. The electrical depolarizations that trigger cardiac myocytes to contract arise spontaneously within the myocyte itself. The heartbeat is initiated in the pacemaker regions and spreads to the rest of the heart through a conduction pathway. Pacemaker cells develop in the primitive atrium and the sinus venosus to form the sinoatrial node and the atrioventricular node respectively. Conductive cells develop the bundle of His and carry the depolarization into the lower heart. The human heart begins beating at a rate near the mother’s, about 75–80 beats per minute (bpm). The embryonic
Cardiac glycoside changes to heart chronotropic activity, resulting in multiple kinds of dysrhythmia and potentially fatal ventricular tachycardia. These dysrhythmias are an effect of an influx of sodium and decrease of resting membrane potential threshold in cardiac muscle cells. When taken beyond a narrow dosage range specific to each particular cardiac glycoside, these compounds can rapidly become dangerous. In sum, they interfere with fundamental processes that regulate membrane potential they are toxic to the heart, the brain, and the gut, at doses that are not difficult to reach. (In the heart, the most common negative effect is Premature ventricular contraction.) Cardiac glycoside