A 60-year-old patient is short of breath and cyanotic. Lung sounds reveal crackles and you note accessory muscle use. You should suspect?

The scenario describes a 60-year-old patient experiencing shortness of breath, cyanosis, crackling lung sounds (evident of fluid in the lungs), and the use of accessory muscles for breathing. These symptoms align most closely with left-sided heart failure.

In left-sided heart failure, the heart is unable to effectively pump blood, leading to fluid accumulation in the lungs, known as pulmonary congestion. This results in crackles upon auscultation due to fluid in the alveoli and can cause hypoxia, evidenced by cyanosis. The increased work of breathing and use of accessory muscles reflects the body's compensatory response to the diminished oxygenation and increased respiratory effort.

The other options are less likely in this context. An asthma attack typically presents with wheezing rather than crackles, primarily due to bronchospasm. Right-sided heart failure would likely lead to symptoms such as peripheral edema and hepatomegaly, rather than pulmonary congestion. A pneumothorax would generally result in unilateral breath sounds and potentially hyper-resonance, which deviates from the findings of crackles and bilateral symptoms seen here. Thus, given the signs and symptoms presented, left-sided heart failure is the most plausible diagnosis.