To solve this problem, we need to understand how parasympathetic neural signals affect the heart's functioning.$\newline$The parasympathetic nervous system primarily influences the heart through the vagus nerve, which releases acetylcholine.$\newline \bullet$Acetylcholine acts on the heart's pacemaker cells, specifically the sinoatrial (SA) node, to decrease the heart rate.$\newline \bullet$A decrease in heart rate leads to a reduction in cardiac output, as cardiac output is the product of heart rate and stroke volume.$\newline$Therefore, parasympathetic stimulation results in:$\newline \bullet$Reduced heart rate$\newline \bullet$Reduced cardiac output$\newline$This analysis corresponds to Option 1: Reduce both heart rate and cardiac output.