The results of a new analysis on the impact of day, month, and hour of admission on inpatient outcomes in more than 900,000 hospitalizations for congestive heart failure were presented during the Heart Failure Congress 2013 of the ESC Heart Failure Association.
The analysis showed that individuals with congestive heart failure are more likely to die when admitted to the hospital in January and February and a Friday, Saturday or Sunday. 

The study included an analysis of 949 907 patients with a primary diagnosis of heart failure hospitalized in New York State between 1994 and 2007. Between 1994 and 2007, in-hospital mortality and the average length of stay for heart failure declined at a rate of 0.3% per year and 0.3 days per year, respectively. Despite the reductions, seasonal trends for heart-failure admissions and mortality were still observed. Peak admissions for heart failure occurred in February, while mortality was highest in January. There is speculation that patients might be sicker in the winter with other illnesses, such as chronic obstructive pulmonary disease or pneumonia, but even after adjustment for these comorbidities in the present analysis, including depression and substance abuse, mortality remained significantly increased in the winter months.
Temperature appears to be responsible for most of the seasonal variation in admissions and mortality. A negative association was observed between ambient temperature and in-hospital mortality, with each 4°C increase associated with a 3% lower risk of death (p<0.0001). With regard to the increased risk of death on the weekend, patients might go unseen by specialists. Time of admission also played a role,  with patients admitted later in the day and evening faring worse than patients admitted between 6 am and 8 am. There is an approximate 50% difference in mortality when comparing those admitted in the early morning vs those admitted in the afternoon/early evening.

Source:
P1230 Heart Failure Congress 2013, Heart Failure Association of the European Society of Cardiology. Impact of day, month, and hour of admission on inpatient outcomes in 949,907 hospitalizations for congestive heart failure D.P. Kao, C.K. Mcilvennan, R.L. Page, R.L. Page, J. Lindenfeld (Denver, US