Diagram showing the Starlings law applied to the left atrium. The force of contraction and A wave magnitude is represented on the vertical axis and the left atrial stretch due to increasing left atrial pressure is represented on the horizontal axis. The different A wave patterns are superimposed on the Starlings curve. The force of contraction (A waves) increases with increasing stretch (left artial pressure) till physiological limit is reached at pattern 1. Beyond that there is progressive left atrial failure.