This has the effect of increasing the resting leakage potassium conductance of the pacemaker cell membrane. This in turn hyperpolarises the pacemaker cells and slows down the pacemaker potential. Hormones Circulating hormones can also affect heart rate. Changes in ion concentration Correct pacemaking requires precise control of ion gradients. Similarly, an elevated external calcium concentration will result in extra calcium influx during the action potential and hence a faster depolarisation rate.
All ion channels open faster as temperature increases.
Thus, increased temperature results in an increased pacemaking rate as the depolarisation rate is increased. Regulation of stroke volume Stroke volume can be regulated by both intrinsic and extrinsic mechanisms. Intrinsic mechanisms are controlled by the heart muscle itself, while extrinsic mechanisms are contolled by external factors. The Frank-Starling law states that the amount of blood pumped out of the heart is proportional to the amount of blood pumped in. In other words, the larger the end diastolic volume, the larger the stroke volume and the larger the strength of contraction.