Substernal chest tightness and shortness of breath for 2 hours. Twenty minutes before the onset of the pain, she had smoked crack cocaine. Her pulse is 110/min, and blood pressure is 170/100 mm Hg. Bilateral basilar crackles are heard. There is an S4 gallop. A nonradiating, grade 2/6, systolic ejection murmur is heard at the upper right sternal border. What is the most likely diagnosis?