Final answer:
Negative inotropic agents, bradycardia, heart failure, and cardiogenic shock can cause decreased myocardial contractility.
Step-by-step explanation:
Decreased myocardial contractility can be caused by various factors. Negative inotropic agents, such as hypoxia, acidosis, hyperkalemia, and certain drugs like beta blockers and calcium channel blockers, can decrease the strength of contraction. Bradycardia, a slow heart rate, can also lead to decreased contractility. In addition, heart failure and cardiogenic shock can impact myocardial contractility.