CVS Practice Test

The primary effect of larger amounts of calcium diffusing into the cardiac myocyte is that it strengthens cardiac muscle contraction. Calcium plays a crucial role in the excitation-contraction coupling process of cardiac muscle cells. When calcium ions enter the myocyte, they bind to troponin, which leads to a series of interactions that cause myosin and actin filaments to slide over each other, resulting in muscle contraction.

Increased calcium availability enhances the strength of each contraction by allowing more cross-bridges to form between actin and myosin, effectively increasing the force of contraction for each heartbeat. This mechanism is fundamental for the heart's ability to pump blood efficiently, especially during activities that demand greater cardiac output, such as exercise or stress.

In contrast, other options such as increased heart rate or decreased oxygen demand do not directly result from the increased influx of calcium. While calcium can have indirect effects on heart rate, its primary and more immediate effect is on the strength of contraction. Reduced contractility, which would imply a decrease in the heart's ability to contract, is contrary to the effect of increased calcium levels, as calcium is known for its role in enhancing cardiac contractility.