Answer: Carlos is "el cardiólogo".
Step-by-step explanation: The Spanish word "cardiólogo" means "cardiologist", which denotes a profession that consists in preventing and treating heart diseases. In the dialogue provided, Carlos expresses that he treats people who suffer from heart diseases ("enfermedades del corazón"); therefore, Carlos is el cardiólogo/the cardiologist. In contrast, "terapista físico" means "physical therapist", "veterinaria" means "veterinarian" and "pediatra" means "pediatrician".