Becoming breathless can be heart related, and that requires urgent attention. Or indicate some pulmonary problem.
But the situation causing this condition needs to be considered. Breathless after taking a single flight of stairs? Or after running a marathon?
I'm dealing with this right now. My husband is showing signs of becoming breathless in ordinary walking. He did previously some years ago, that was remedied with a heart bypass operation. (That I personally ordered be done. We both having mutual legal arrangements that give us full medical authority over each other) Now those previous symptoms may be returning.
Naturally I had him do a heart-stress test at his cardiologist's right after we returned from his older brother's Boston funeral 3 weeks ago, and we'll be getting those results shortly. You have to stay on top of these things if you wanna stay alive.
So yeah, becoming breathless is a real attention getter. Are you overweight? Sedentary? Young or older? Is this a recent change? Lots of variables & questions. See a doctor!