Yes, having two heart lines (or a doubled line) is a rare trait present in about 5% of people. It generally indicates very high emotional intensity, an ability to love on two different registers, or a split between assumed feelings and secret emotions that coexist without mixing.
How to recognize it
The double heart line appears as two parallel tracings below the base of the fingers, instead of just one.
The upper line, closer to the fingers, is generally the main one. The second, finer and lower, runs parallel along part or all its length.
What tradition says
Two heart lines signal a person who feels doubly. Love crosses them on two frequencies at once: the visible sentiment and the deep emotion that doubles it.
Some palmists see it as the mark of people who can love two people differently without lying, or hold passion and tenderness together without confusing them.
Nuances by tracing
If the second line is shorter, it acts as reinforcement: ability to love strongly, once, for a long time.
If it's as long as the main one, the heart really lives on two planes, often in artists, caregivers, multiple personalities.
If it's broken while the first is continuous, a secret or unfinished story doubles an official one.
Is it luck?
Neither luck nor curse. The double heart line says above all that you love in a complex way, rarely simple, rarely lukewarm.