**8. Heart rate**

Increase in the frequency of contraction increases C.O at a given filling pressure. This is called the staircase (Bowditch) effect. Reduction in diastolic time can result in reduction of ventricular filling, thus limiting C.O increase with tachycardia. An important corollary to remember is that the filling of coronary arteries takes place in diastole and tachycardia can compromise diastolic coronary filling.
