When you focus on the third chakra it has to pull the kundalini from the root center, through the second, up to the third chakra.
It is not advisable for persons who are in the early stages of meditation to mediate on the two lower chakras. You will unleash powers and forces that will throw you into very powerful altered state of consciousness that might not be pleasant at all.
Focus on the center of the chest, relax. Imagine a rose there. Feel it unfolding. Let yourself go and ignore your thoughts.
As you focus your attention on the heart center, you will begin to feel your thoughts slowing down. You'll begin to feel your mind becoming calm and quiet. They won't bother you.
Sensations of peace, joy, and love will enter into you. They will be very subtle at first. Then they will grow stronger.
There is no end to the petals of the inner rose. Continue to unfold set after set of petals until you have completed your meditation session.