Altruistic love turn into compassion when confronted with the suffering of others. Compassion is the wish that others may be free from suffering and its causes. For this to happen, we must be concerned about the fate of the other, be aware of their sufferings, wish that these be healed, and be ready to do whatever is possible to do so.
To generate compassion, imagine a loved one who is experiencing excruciating physical or mental pain. Deeply her suffering as if it was your own, until this becomes unbearable.
At this point, turn to an unconditional feeling of love for this person. Imagine taking gently the person in your arms. Visualize that every atom of her suffering is now filled with an atom of love. Wish from my heart that this person may be free from suffering.
Then extend this warm and courageous compassion to other beings who are dear to you; then to strangers and to all sentient beings.