In Anton Chekov's The Bear, I think there are two distinctions in the play with regard to "affairs of the heart."

First, Popova venerates the memory of her dead husband, but not out of love. He was a terrible man, cheating on her and making fun of her, but she is determined to "show" him in death, how dedicated she was and remains, for the rest of her life. There is no love in this scenario: only Popova's need to prove (perhaps mostly to herself) that she had value in the marriage.

When Smirnov enters, romance is nowhere to be found. He is there to collect a debt, which he desperately needs and Popova is unable to give him what he wants. This parallels their early interaction: he has a hardened heart with regard to women, but Popova is in no place in her life where she can help him—or would even consider it: as we see when he tells her he "likes" her. To himself he notes:

SMIRNOV. 
I absolutely like her! Absolutely! Even though her cheeks are dimpled, I like her! I'm almost ready to let the debt go... and I'm not angry any longer.... Wonderful woman!

When he refuses to hurt her, she demands to know why. Is he afraid? Finally he admits how he feels and she is intensely insulted:

POPOVA. 
You lie! Why won't you fight?

SMIRNOV.
 Because... because you... because I like you.

POPOVA. 
[Laughs]

He likes me! He dares to say that he likes me!

However, it would seem that Chekov is saying that romance is like nature: unpredictable. It does not always come easily, perhaps satirizing the idea of love at first sight. Chekov may also be making note that there is a "fine line between love and hate," for at one moment Smirnov is ready to duel...

SMIRNOV. 
It's about time we got rid of the prejudice that only men need pay for their insults. Devil take it, if you want equality of rights you can have it. We're going to fight it out!

POPOVA. 
With pistols? Very well!

The more passionate she becomes to kill him (perhaps her way of taking out her frustrations she harbors because of her worthless marriage), the more intrigued Smirnov becomes: she is not like the simpering women he has known in the past, putting on fragile airs and using the men around them. In recognizing this, Chekov allows Smirnov to confirm in Popova the very things she has been trying to find within herself, to feel worthier than her husband ever gave her credit for being.

And just as quickly as he was ready to duel, now Smirnov has fallen in love with Popova and sweeps her off her feet.

SMIRNOV. 
[Approaching her]

How angry I am with myself! I'm in love like a student, I've been on my knees....

…[Puts his arms around her] 
I shall never forgive myself for this....

POPOVA. 
Get away from me! Take your hands away! I hate you! Let's go and fight!

[A prolonged kiss…]

Romance, Chekov seems to tell the audience, is not an easy affair, but neither is it as impossible as it may first seem—at least when the "right" people are involved.