Hi. Welcome to HealingWell.
An echocardiogram is a study of the heart using ultrasound. A bubble echocardiogram is an extension of this that uses simple air bubbles as a contrast medium during this study and often has to be requested specifically. Although colour Doppler can be used to detect abnormal flows between the chambers of the heart (e.g. patent foramen ovale) it has a limited sensitivity. When specifically looking for a defect such as this small air bubbles can be used as a contrast medium and injected intravenously, where they travel to the right side of the heart. The test would be positive for an abnormal communication if the bubbles are seen passing into the left side of the heart. (Normally they would exit the heart through the pulmonary artery and be stopped by the lungs.) This form of bubble contrast medium is generated on an ad hoc basis by the testing clinician by agitating normal saline (e.g. by rapidly and repeatedly transferring the saline between two connected syringes) immediately prior to injection.
I'm not sure a Echocardiogram with contrast is any more than described above. I've had this one done. If you were in heart failure, a common symptom would be fluid accumulation in your lower legs, ankles, and feet. Have you noticed this? You're looking pretty healthy by the tests you've already had done, if your cardiologist felt the contrast was imperative, he/she would likely reschedule the test. Did they tell you what the chest pain may have been caused by?