What effect do beta 1 receptors have on the heart?

Beta 1 receptors are primarily located in the heart and are responsible for mediating several key cardiac functions. When activated, they lead to an increase in heart muscle contraction strength, also known as positive inotropic effect. This enhancement of contractility is crucial during times of increased demand for blood flow, such as during exercise or stress.

Additionally, stimulation of beta 1 receptors also contributes to an increase in heart rate, known as a positive chronotropic effect, due to their influence on the sinoatrial (SA) node. However, the key focus here is the effect on heart muscle contraction, which is why the choice highlighting the increase in heart muscle contraction accurately reflects the primary action attributed to beta 1 receptors in the cardiovascular system. Other options refer to effects not associated with beta 1 receptors, such as bronchial smooth muscle relaxation, decreased heart rate, or stimulation of salivation, which are mediated by other receptor types.