My first patient after lunch was Lu Chen, a 45-year-old new patient who was scheduled for his first periodontal SRP with anesthesia appointment

My first patient after lunch was Lu Chen, a 45-year-old new patient who was scheduled for his first periodontal SRP with anesthesia appointment. He is a 5’11” Asian male weighing 227lbs. Mr. Chen just moved to the United States and has never had dental hygiene care. He was a chain smoker and never took care of his oral hygiene as it was not important to him.
After reviewing his medical history, I found out that he had a cardiac episode in 6 months ago. He also smokes one pack of cigarettes a day and is taking Effexor for anxiety. His vital signs were as follows: pulse 82, respiration 16, and blood pressure 140/86. He said he usually has no symptoms regarding his cardiac episodes.
After reviewing Mr. Chen’s case, he presented with generalized chronic moderate periodontitis with heavy tenacious calculus throughout the dentition. I completed the ultrasonic scaling on the mandibular right quadrant and began the hand scaling procedure. It was necessary for me to put a great deal of pressure in order to remove all of the remaining deposits. I used the Nevi 2 scaler interproximally on teeth 29 and 30. During the treatment, I noticed that he was showing shortness of breath and was sweating. He suddenly complained of chest pain and started squeezing his chest, saying ‘My chest feels tight.’ Mr. Chen’s pulse was very weak. He also became nauseous, and was turning blue and eventually stopped breathing.

Considering the facts presented, please make an educated guess as to what medical emergency is being played out/described
Please list two (2) actions, that should be taken (by the clinician), in response to the medical emergency you believe to be taking place