Dear All My co-authors and I would like to share our recent publication measuring cardiovascular responses in the bottlenose dolphin during breath-holds at rest. In this paper we measure heart rate and stroke volume and calculate cardiac output. We correct the values for the cofounding changes in cardiac function associated with each breath, the Respiratory Sinus Arrhythmia, and conclude that the dive response is minimal. We propose that in the dolphin, the dive response (reduced heart rate and cardiac output) is an extension of the Respiratory Sinus Arrhythmia and a more generalized physiological response and not a specialized trait for diving. We also provide results that suggest that dolphins can voluntarily alter heart rate and blood flow. This mechanism would allow them to adjust blood flow based on the dive they are planning, and adjust flow during the dive to alter changes due to metabolic demand. Voluntary adjustment of heart rate has been shown previously in other species, such as the harbor porpoise or sea lion, and a limited ability for such an adjustment have also been shown in human elite athletes. We propose that this ability to voluntary alter blood flow as needed during the dive is the key adaptation how they match demand and supply, and may explain how failure of this mechanism during stress can cause diving related issues such as the bends. While controversial, this new article questions the importance of the dive response that has for long been thought to be one of the main mechanisms for how diving animals can perform extended breath-holds, and argues that evolution has enabled dolphins and marine mammals to become efficient at voluntary adjustment of heart rate and blood flow to improve use of the available oxygen. For anyone interested in this Open Access publication, the details and a link are below, or send me an email at afahlman@whoi.edu <mailto:afahlman@whoi.edu> for a pdf, or for questions of comments. Sincerely, Andreas Title:Re-evaluating the significance of the dive response during voluntary surface apneas in the bottlenose dolphin, Tursiops truncatus Authors:Fahlman, A.,Miedler, S., Rocho-Levine, J., Jabois, A., Arenarez, J., Marti-Bonmati, L., García-Párraga, D., Cauture, F. Journal: Scientific Reports, 9, DOI: 10.1038/s41598-019-45064-8 URL: www.nature.com/articles/s41598-019-45064-8 Abstracts: The dive response is well documented for marine mammals, and includes a significant reduction in heart rate (fH) during submersion as compared while breathing at the surface. In the current study we assessed the influence of the Respiratory Sinus Arrhythmia (RSA) while estimating the resting fH while breathing. Using transthoracic echocardiography we measured fH, and stroke volume (SV) during voluntary surface apneas at rest up to 255 s, and during recovery from apnea in 11 adult bottlenose dolphins (Tursiops truncatus, 9 males and 2 females, body mass range: 140-235 kg). The dolphins exhibited a significant post-respiratory tachycardia and increased SV. Therefore, only data after this RSA had stabilized were used for analysis and comparison. The average (± s.d.) fH, SV, and cardiac output (CO) after spontaneous breaths while resting at the surface were 44 ± 6 beats min-1, 179 ± 31 ml, and 7909 ± 1814 l min-1, respectively. During the apnea the fH, SV, and CO decreased proportionally with the breath-hold duration, and after 255 s they, respectively, had decreased by an average of 18%, 1-21%, and 12-37%. During recovery, the fH, SV, and CO rapidly increased by as much as 117%, 34%, and 190%, respectively. Next, fH, SV and CO rapidly decreased to resting values between 90-110 s following the surface apnea. These data highlight the necessity to define how the resting fH is estimated at the surface, and separating it from the RSA associated with each breath to evaluate the significance of cardiorespiratory matching during diving.