The side-effects of compassion are plentiful, according to David Hamilton PhD: compassion causes growth on the left side of the prefrontal cortex region. The effect is we find it easier to be compassionate and kind. Compassion begets compassion by creating actual changes in the brain.
Compassion also boosts oxytocin, a key hormone responsible for heart health by reducing blood pressure and dilating our arteries. Oxytocin is a feel good hormone which, when released, fosters our emotional connection, is good for the heart and enhances relationships.