What Could Be The Cause Of My Wife S Ongoing Breathlessness And Chest Constriction After Coronavirus?

Hello. Several days ago my wife experienced sudden symptoms of chest constriction, shortness of breath, light-headed. Went to ER. Blood test normal. Blood oxygen consistently 98%. Pulse 60ish. Came home. Last 4 days increased breathlessness. Still 98% Blood Oxygen. Still Pulse 60ish. We re being seen by a cardiologist today. Any possible idea re diagnosis? She had COVID in October. Thank you.