So remember, the action potential of skeletal muscles looks like this. But the action potential for cardiac muscle looks like this, because we have this extended period known as our plateau phase. So basically, in this case, our comparison between the graph or the action potential on the membrane and the muscle contraction looks something like this, which is slightly different. We see that the muscle actually begins to contract before our action potential has finished. So basically, when we're somewhere in between our plateau phase, that's when our muscle contraction basically almost reaches the highest portion. So about when we reach this point here does our muscle contraction actually begin to take place.