'Heirs' revealed how its cast members survive their tough filming schedule with behind-the-scenes photos of their cat naps.

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Lee Min Ho and Park Shin Hye, who have the most dialogue among the cast as the lead stars, have been revealed to get through their filming with 2-3 hours of sleep daily, while�Kim Woo Bin�can be seen using his five-minute break to rest up for his next scene. Park Shin Hye also brought laughs by sharing a candid camera shot of Hyungsik falling asleep and looking adorable.

A rep commented, "The cast of 'Heirs' survive their all-night filming with just a brief nap on set, but they don't show their tiredness and carry out their filming rigorously... Please anticipate the top actors who show their fighting spirit with a sense of responsibility and passion to create a high quality drama."

Their hard work seems to have definitely paid off as the drama surpassed the 20% viewer rating mark last week!