Bowditch effect

The Bowditch effect (Treppe effect, staircase phenomenon) is one of the mechanisms of homeometric regulation of the heart.
 * At a higher heart rate, the sodium-calcium pump is not enough to pump Ca2+ ions out of the cell to the original state.
 * The concentration of ions gradually increases, which is manifested by positive inotropia (increased  force of contraction).

Related articles

 * Homeometric regulation of the heart
 * Frank-Starling mechanism