How did Gu discover that Lu Youyan had a heart attack in The Road Is White Tonight?

In the novel Tonight's Road to White, Gu and Lu Youyan still love each other very much, so even if the other party still hides something from themselves, they still intend to live like this and even get married.

Then, because Gu gave Lu Youyan too much uncertainty, when Gu went out and didn't tell Lu Youyan what he was going to do, Lu Youyan accidentally saw the text message sent to Gu by Zhou Huai 'an, thinking that Gu was going to Zhou Huai 'an for an appointment. Afraid of his accident, Lu Youyan also went out to the tea shop.

Before the results came out, I found that Gu's company was on fire, and I met Zhou Huai 'an. I asked Zhou Huai 'an where Bai Ye was. Zhou Huai 'an bears a grudge and says that Gu is in the fire again. Lu Youyan loved Bai Ye so much that he believed it, so he went into the fire alone and went up dozens of floors. As a result, he had a heart attack and was smoked until he fainted. Gu saw the fire and knew that everything was in his plan. When I was happy, I suddenly saw the fire watcher holding Lu Youyan's necklace in his hand, and my heart trembled. After knowing that Lu Youyan went in, he went in without hesitation.

I saw Lu Youyan on the stairs. At that time, Lu Youyan was dying, and I couldn't take the medicine out. I can only ask Gu Bai Ye to help me. Bai Ye knew that Lu Youyan had a heart attack. . . .